diff --git a/applications/utilities/parallelProcessing/redistributePar/loadOrCreateMesh.C b/applications/utilities/parallelProcessing/redistributePar/loadOrCreateMesh.C
index 95522b56c6..aae5cedb13 100644
--- a/applications/utilities/parallelProcessing/redistributePar/loadOrCreateMesh.C
+++ b/applications/utilities/parallelProcessing/redistributePar/loadOrCreateMesh.C
@@ -162,9 +162,8 @@ Foam::boolList Foam::haveMeshFile
         handler.filePath(runTime.path()/meshPath/meshFile)
     );
 
-    bool found = (!fName.empty() && handler.isFile(fName));
-
-    if (found)
+    bool found = handler.isFile(fName);
+    if (returnReduceAnd(found)) // worldComm
     {
         autoPtr<ISstream> isPtr(fileHandler().NewIFstream(fName));
         if (isPtr && isPtr->good())
diff --git a/src/OpenFOAM/db/Time/Time.C b/src/OpenFOAM/db/Time/Time.C
index e4912421da..2b1673a1f5 100644
--- a/src/OpenFOAM/db/Time/Time.C
+++ b/src/OpenFOAM/db/Time/Time.C
@@ -202,7 +202,8 @@ void Foam::Time::setControls()
     //       alternative processorsDDD directories naming
     //       - do not look for compressed (is directory)
 
-    if (fileHandler().filePath(timePath(), false).empty())
+    const fileName timeDir(fileHandler().filePath(timePath(), false));
+    if (returnReduceAnd(timeDir.empty()))
     {
         const int oldPrecision = precision_;
         int requiredPrecision = -1;
@@ -225,7 +226,8 @@ void Foam::Time::setControls()
             oldTime = std::move(newTime);
 
             // Does a time directory exist with the new format?
-            if (!fileHandler().filePath(timePath(), false).empty())
+            const fileName timeDir(fileHandler().filePath(timePath(), false));
+            if (returnReduceOr(!timeDir.empty()))
             {
                 requiredPrecision = precision_;
             }
diff --git a/src/OpenFOAM/global/fileOperations/collatedFileOperation/collatedFileOperation.C b/src/OpenFOAM/global/fileOperations/collatedFileOperation/collatedFileOperation.C
index 22a2a5616b..be88c0c135 100644
--- a/src/OpenFOAM/global/fileOperations/collatedFileOperation/collatedFileOperation.C
+++ b/src/OpenFOAM/global/fileOperations/collatedFileOperation/collatedFileOperation.C
@@ -113,43 +113,7 @@ void Foam::fileOperations::collatedFileOperation::printBanner
 
     if (withRanks)
     {
-        // Information about the ranks
-        stringList hosts(Pstream::nProcs());
-        if (Pstream::master(comm_))
-        {
-            hosts[Pstream::myProcNo()] = hostName();
-        }
-        Pstream::gatherList(hosts);
-
-        DynamicList<label> offsetMaster(Pstream::nProcs());
-
-        forAll(hosts, ranki)
-        {
-            if (!hosts[ranki].empty())
-            {
-                offsetMaster.append(ranki);
-            }
-        }
-
-        if (offsetMaster.size() > 1)
-        {
-            DetailInfo
-                << "IO nodes:" << nl << '(' << nl;
-
-            offsetMaster.append(Pstream::nProcs());
-
-            for (label group = 1; group < offsetMaster.size(); ++group)
-            {
-                const label beg = offsetMaster[group-1];
-                const label end = offsetMaster[group];
-
-                DetailInfo
-                    << "    (" << hosts[beg].c_str() << ' '
-                    << (end-beg) << ')' << nl;
-            }
-            DetailInfo
-                << ')' << nl;
-        }
+        fileOperation::printRanks();
     }
 
     //- fileModificationChecking already set by base class (masterUncollated)
diff --git a/src/OpenFOAM/global/fileOperations/fileOperation/fileOperation.C b/src/OpenFOAM/global/fileOperations/fileOperation/fileOperation.C
index 059aa20391..bbca362e0d 100644
--- a/src/OpenFOAM/global/fileOperations/fileOperation/fileOperation.C
+++ b/src/OpenFOAM/global/fileOperations/fileOperation/fileOperation.C
@@ -80,6 +80,7 @@ Foam::word Foam::fileOperation::processorsBaseDir = "processors";
 //- Caching (e.g. of time directories) - enabled by default
 int Foam::fileOperation::cacheLevel_(1);
 
+int Foam::fileOperation::nProcsFilter_(0);
 
 // * * * * * * * * * * * * * * * Local Functions * * * * * * * * * * * * * * //
 
@@ -179,8 +180,6 @@ static bool parseProcsNumRange
 } // End anonymous namespace
 
 
-#if 0
-
 // Sorting of processor directories
 #include "stringOpsSort.H"
 namespace
@@ -214,7 +213,6 @@ void sortProcessorDirs(Foam::UList<Foam::fileOperation::dirIndex>& dirs)
 }
 
 } // End anonymous namespace
-#endif
 
 
 // * * * * * * * * * * * * * Static Member Functions * * * * * * * * * * * * //
@@ -432,6 +430,16 @@ Foam::fileOperation::lookupAndCacheProcessorsPath
     // - distributed() : different processors have different roots
     // - fileModificationChecking : (uncollated only) do IO on master only
 
+
+    // Collated : check whether/how to filter processorsXXX directory names
+    const label targetNProcs
+    (
+        (UPstream::parRun() && nProcsFilter_ < 0)
+      ? UPstream::nProcs(UPstream::worldComm)
+      : nProcsFilter_
+    );
+
+
     fileName path, pDir, local;
     procRangeType group;
     label numProcs;
@@ -528,6 +536,19 @@ Foam::fileOperation::lookupAndCacheProcessorsPath
             }
             else if (rNum != -1)
             {
+                if (targetNProcs > 1 && (targetNProcs != rNum))
+                {
+                    // Current directory can never contain wanted proc
+                    //Pout<< "For fName:" << fName
+                    //    << "Ignoring directory " << dirN
+                    //    << " since parsed rNum:" << rNum
+                    //    << " targetNProcs:" << targetNProcs
+                    //   << endl;
+                    //error::printStack(Pout);
+
+                    continue;
+                }
+
                 // "processorsNN" or "processorsNN_start-end"
                 nProcs = max(nProcs, rNum);
 
@@ -571,7 +592,7 @@ Foam::fileOperation::lookupAndCacheProcessorsPath
         if (debug)
         {
             Pout<< "fileOperation::lookupProcessorsPath " << procPath
-                << " detected:" << procDirs << endl;
+                << " detected:" << flatOutput(procDirs) << endl;
         }
 
         if (UPstream::parRun() && (!distributed() || syncPar))
@@ -655,7 +676,7 @@ Foam::fileOperation::lookupAndCacheProcessorsPath
         }
 
         // Sort processor directory names (natural order)
-        /// sortProcessorDirs(procDirs);
+        sortProcessorDirs(procDirs);
 
         if (procDirsStatus & 2u)
         {
@@ -680,7 +701,6 @@ Foam::fileOperation::lookupAndCacheProcessorsPath
 Foam::refPtr<Foam::fileOperation::dirIndexList>
 Foam::fileOperation::lookupProcessorsPath(const fileName& fName) const
 {
-    // Use parallel synchronisation
     return lookupAndCacheProcessorsPath(fName, true);
 }
 
@@ -844,6 +864,7 @@ Foam::fileName Foam::fileOperation::filePath
     }
 
     // Give preference to processors variant
+    fileName foundName;
     if (proci != -1)
     {
         // Get all processor directories
@@ -859,26 +880,40 @@ Foam::fileName Foam::fileOperation::filePath
                 {
                     Pout<< "fileOperation::filePath : " << collatedName << endl;
                 }
-                return collatedName;
+                foundName = collatedName;
             }
         }
     }
 
-    if (exists(fName, checkGzip, followLink))
+    //if (returnReduceOr(foundName.empty()))    // worldComm
+    if (foundName.empty())
+    {
+        // There is at least one processor that cannot find the processors
+        // directory. Re-do with straight supplied filename
+        if (exists(fName, checkGzip, followLink))
+        {
+            if (foundName.empty())
+            {
+                foundName = fName;
+            }
+        }
+    }
+
+    if (!foundName.empty())
     {
         if (debug)
         {
-            Pout<< "fileOperation::filePath : " << fName << endl;
+            Pout<< "fileOperation::filePath : " << foundName << endl;
         }
-        return fName;
     }
-
-    if (debug)
+    else
     {
-        Pout<< "fileOperation::filePath : Not found" << endl;
+        if (debug)
+        {
+            Pout<< "fileOperation::filePath : Not found" << endl;
+        }
     }
-
-    return fileName();
+    return foundName;
 }
 
 
diff --git a/src/OpenFOAM/global/fileOperations/fileOperation/fileOperation.H b/src/OpenFOAM/global/fileOperations/fileOperation/fileOperation.H
index 0bf282312d..5de0a2a149 100644
--- a/src/OpenFOAM/global/fileOperations/fileOperation/fileOperation.H
+++ b/src/OpenFOAM/global/fileOperations/fileOperation/fileOperation.H
@@ -150,6 +150,13 @@ private:
         //- Storage of the dummy file handler (demand-driven)
         static refPtr<fileOperation> dummyHandlerPtr_;
 
+        //- Filtering of processorsDDD directories (in parallel):
+        //      - >0 : only accept processorsDDD (default)
+        //      -  0 : accept anything (e.g. when detecting nprocs from
+        //             directory naming)
+        //      - -1 : use nProcs(UPstream::worldComm)
+        static int nProcsFilter_;
+
 
 protected:
 
@@ -452,6 +459,21 @@ public:
             return old;
         }
 
+        //- Return collated 'processorsDDD' filtering
+        static int nProcsFilter() noexcept
+        {
+            return nProcsFilter_;
+        }
+
+        //- Set collated 'processorsDDD' filtering (0 = off).
+        //  \return the previous value
+        static int nProcsFilter(int level) noexcept
+        {
+            int old(nProcsFilter_);
+            nProcsFilter_ = level;
+            return old;
+        }
+
         //- Sort directory entries according to time value,
         //  with "constant" appearing first (if it exists)
         static instantList sortTimes
diff --git a/src/OpenFOAM/global/fileOperations/fileOperation/fileOperationNew.C b/src/OpenFOAM/global/fileOperations/fileOperation/fileOperationNew.C
index b12739ed76..7b0af4fdfd 100644
--- a/src/OpenFOAM/global/fileOperations/fileOperation/fileOperationNew.C
+++ b/src/OpenFOAM/global/fileOperations/fileOperation/fileOperationNew.C
@@ -383,7 +383,9 @@ Foam::fileOperation::New_impl
 
         if (newHandler)
         {
-            newHandler->nProcs(origHandler.nProcs());
+            // Make sure that the output format uses the correct number of
+            // 'active' ranks (instead of that of the origHandler)
+            newHandler->nProcs(subProcs.size());
             newHandler->storeComm();
         }
     }
@@ -402,7 +404,30 @@ Foam::fileOperation::New
 {
     labelList subProcs = getSelectedProcs(useProc);
 
-    return fileOperation::New_impl(origHandler, subProcs, verbose);
+    // useProc subsets worldComm ranks. So we cannot use worldComm
+    // anywhere in file handler. Workaround: use temporary communicator
+    // so we can at least construct. TBD.
+
+    label oldWorldComm = -1;
+    autoPtr<UPstream::communicator> subWorldComm;
+    if (subProcs.size() != UPstream::nProcs(UPstream::worldComm))
+    {
+        subWorldComm.reset
+        (
+            new UPstream::communicator
+            (
+                UPstream::worldComm,
+                subProcs
+            )
+        );
+        oldWorldComm = UPstream::commWorld(subWorldComm());
+    }
+
+    autoPtr<fileOperation> fh(New_impl(origHandler, subProcs, verbose));
+
+    UPstream::commWorld(oldWorldComm);
+
+    return fh;
 }
 
 
@@ -416,7 +441,31 @@ Foam::fileOperation::New
 {
     labelList subProcs = getSelectedProcs(useProc);
 
-    return fileOperation::New_impl(origHandler, subProcs, verbose);
+    label oldWorldComm = -1;
+    autoPtr<UPstream::communicator> subWorldComm;
+
+    // useProc subsets worldComm ranks. So we cannot use worldComm
+    // anywhere in file handler. Workaround: use temporary communicator
+    // so we can at least construct. TBD.
+
+    if (subProcs.size() != UPstream::nProcs(UPstream::worldComm))
+    {
+        subWorldComm.reset
+        (
+            new UPstream::communicator
+            (
+                UPstream::worldComm,
+                subProcs
+            )
+        );
+        oldWorldComm = UPstream::commWorld(subWorldComm());
+    }
+
+    autoPtr<fileOperation> fh(New_impl(origHandler, subProcs, verbose));
+
+    UPstream::commWorld(oldWorldComm);
+
+    return fh;
 }
 
 
diff --git a/src/OpenFOAM/global/fileOperations/fileOperation/fileOperationRanks.C b/src/OpenFOAM/global/fileOperations/fileOperation/fileOperationRanks.C
index 318afc65e5..c500571412 100644
--- a/src/OpenFOAM/global/fileOperations/fileOperation/fileOperationRanks.C
+++ b/src/OpenFOAM/global/fileOperations/fileOperation/fileOperationRanks.C
@@ -100,8 +100,6 @@ Foam::labelRange Foam::fileOperation::subRanks(const labelUList& mainIOranks)
         }
     }
 
-    Pout<< "subRanks: " << labelRange(begProc, (endProc-begProc)) << endl;
-
     return labelRange(begProc, (endProc-begProc));
 }
 
diff --git a/src/OpenFOAM/global/fileOperations/uncollatedFileOperation/uncollatedFileOperation.C b/src/OpenFOAM/global/fileOperations/uncollatedFileOperation/uncollatedFileOperation.C
index 01103eecee..35fb161016 100644
--- a/src/OpenFOAM/global/fileOperations/uncollatedFileOperation/uncollatedFileOperation.C
+++ b/src/OpenFOAM/global/fileOperations/uncollatedFileOperation/uncollatedFileOperation.C
@@ -121,12 +121,11 @@ Foam::fileName Foam::fileOperations::uncollatedFileOperation::filePathInfo
             // Check if parallel "procesors" directory
             if (io.time().processorCase())
             {
-                refPtr<dirIndexList> pDirs
+                const refPtr<dirIndexList> pDirs
                 (
-                    fileOperation::lookupAndCacheProcessorsPath
+                    lookupProcessorsPath
                     (
-                        io.objectPath(),
-                        false // No additional parallel synchronisation
+                        io.objectPath()
                     )
                 );
 
diff --git a/src/OpenFOAM/global/fileOperations/uncollatedFileOperation/uncollatedFileOperation.H b/src/OpenFOAM/global/fileOperations/uncollatedFileOperation/uncollatedFileOperation.H
index 9b8bd51083..ae9fc3d10e 100644
--- a/src/OpenFOAM/global/fileOperations/uncollatedFileOperation/uncollatedFileOperation.H
+++ b/src/OpenFOAM/global/fileOperations/uncollatedFileOperation/uncollatedFileOperation.H
@@ -85,7 +85,7 @@ protected:
         //  \return empty fileName if not found.
         virtual refPtr<dirIndexList> lookupProcessorsPath
         (
-            const fileName&
+            const fileName& objectPath
         ) const;
 
 
diff --git a/src/finiteVolume/fvMesh/fvMeshTools/fvMeshTools.C b/src/finiteVolume/fvMesh/fvMeshTools/fvMeshTools.C
index 14f154017d..b9280f819b 100644
--- a/src/finiteVolume/fvMesh/fvMeshTools/fvMeshTools.C
+++ b/src/finiteVolume/fvMesh/fvMeshTools/fvMeshTools.C
@@ -794,25 +794,6 @@ Foam::fvMeshTools::loadOrCreateMeshImpl
         // Non-null reference when a mesh exists on given processor
         haveLocalMesh = (*readHandlerPtr).good();
     }
-    else
-    {
-        // No file handler.
-        // Check for presence of the "faces" file,
-        // but for 'decompose', only need mesh on master.
-
-        haveLocalMesh =
-        (
-            decompose
-          ? UPstream::master()
-          : fileHandler().isFile
-            (
-                fileHandler().filePath
-                (
-                    io.time().path()/io.instance()/meshSubDir/"faces"
-                )
-            )
-        );
-    }
 
     // Globally consistent information about who has a mesh
     boolList haveMesh
@@ -820,6 +801,11 @@ Foam::fvMeshTools::loadOrCreateMeshImpl
         UPstream::allGatherValues<bool>(haveLocalMesh)
     );
 
+    // Make sure all have the same number of processors
+    label masterNProcs = fileHandler().nProcs();
+    Pstream::broadcast(masterNProcs);
+    const_cast<fileOperation&>(fileHandler()).nProcs(masterNProcs);
+
 
     autoPtr<fvMesh> meshPtr;
 
@@ -960,6 +946,7 @@ Foam::fvMeshTools::loadOrCreateMeshImpl
             )
         )
         {
+            const_cast<fileOperation&>(fileHandler()).nProcs(UPstream::nProcs(oldWorldComm));
             // Can use the handler communicator as is.
             UPstream::commWorld(fileHandler().comm());
         }