diff --git a/ApplicationLibCode/ProjectDataModel/Polygons/RimPolygonCollection.cpp b/ApplicationLibCode/ProjectDataModel/Polygons/RimPolygonCollection.cpp
index 47af463ba8..f8473d321c 100644
--- a/ApplicationLibCode/ProjectDataModel/Polygons/RimPolygonCollection.cpp
+++ b/ApplicationLibCode/ProjectDataModel/Polygons/RimPolygonCollection.cpp
@@ -63,25 +63,6 @@ RimPolygonCollection* RimPolygonCollection::createTopmost()
     return coll;
 }
 
-//--------------------------------------------------------------------------------------------------
-///
-//--------------------------------------------------------------------------------------------------
-void RimPolygonCollection::loadData()
-{
-    for ( auto* sub : subCollections() )
-    {
-        if ( !sub ) continue;
-        if ( auto* file = dynamic_cast<RimPolygonFile*>( sub ) )
-        {
-            file->loadData();
-        }
-        else if ( auto* coll = dynamic_cast<RimPolygonCollection*>( sub ) )
-        {
-            coll->loadData();
-        }
-    }
-}
-
 //--------------------------------------------------------------------------------------------------
 ///
 //--------------------------------------------------------------------------------------------------
diff --git a/ApplicationLibCode/ProjectDataModel/Polygons/RimPolygonCollection.h b/ApplicationLibCode/ProjectDataModel/Polygons/RimPolygonCollection.h
index d56a036c5d..cc07044680 100644
--- a/ApplicationLibCode/ProjectDataModel/Polygons/RimPolygonCollection.h
+++ b/ApplicationLibCode/ProjectDataModel/Polygons/RimPolygonCollection.h
@@ -39,7 +39,6 @@ public:
     // constructor.
     static RimPolygonCollection* createTopmost();
 
-    void        loadData();
     RimPolygon* createUserDefinedPolygon();
     RimPolygon* appendUserDefinedPolygon();
     void        addUserDefinedPolygon( RimPolygon* polygon );
diff --git a/ApplicationLibCode/ProjectDataModel/Polygons/RimPolygonContainer.cpp b/ApplicationLibCode/ProjectDataModel/Polygons/RimPolygonContainer.cpp
index 40c9417b2a..e314bb9347 100644
--- a/ApplicationLibCode/ProjectDataModel/Polygons/RimPolygonContainer.cpp
+++ b/ApplicationLibCode/ProjectDataModel/Polygons/RimPolygonContainer.cpp
@@ -43,3 +43,14 @@ RimPolygonContainer* RimPolygonContainer::addNewSubCollection()
     addSubCollection( sub );
     return sub;
 }
+
+//--------------------------------------------------------------------------------------------------
+///
+//--------------------------------------------------------------------------------------------------
+void RimPolygonContainer::loadData()
+{
+    for ( auto* sub : subCollections() )
+    {
+        if ( sub ) sub->loadData();
+    }
+}
diff --git a/ApplicationLibCode/ProjectDataModel/Polygons/RimPolygonContainer.h b/ApplicationLibCode/ProjectDataModel/Polygons/RimPolygonContainer.h
index 83886b1985..d5b03dfa1f 100644
--- a/ApplicationLibCode/ProjectDataModel/Polygons/RimPolygonContainer.h
+++ b/ApplicationLibCode/ProjectDataModel/Polygons/RimPolygonContainer.h
@@ -44,4 +44,8 @@ public:
     // the return type stays at RimPolygonContainer* to avoid pulling RimPolygonCollection.h into
     // this header (which would create an include cycle).
     RimPolygonContainer* addNewSubCollection() override;
+
+    // Default behavior recurses into sub-collections. Leaf containers (e.g., file-backed)
+    // override to load their own data; folder containers inherit the recursion.
+    virtual void loadData();
 };
diff --git a/ApplicationLibCode/ProjectDataModel/Polygons/RimPolygonFile.cpp b/ApplicationLibCode/ProjectDataModel/Polygons/RimPolygonFile.cpp
index 5f2cf32e78..808e5fba7c 100644
--- a/ApplicationLibCode/ProjectDataModel/Polygons/RimPolygonFile.cpp
+++ b/ApplicationLibCode/ProjectDataModel/Polygons/RimPolygonFile.cpp
@@ -140,6 +140,14 @@ QString RimPolygonFile::name() const
     return fileInfo.fileName();
 }
 
+//--------------------------------------------------------------------------------------------------
+///
+//--------------------------------------------------------------------------------------------------
+bool RimPolygonFile::canAddSubCollection() const
+{
+    return false;
+}
+
 //--------------------------------------------------------------------------------------------------
 ///
 //--------------------------------------------------------------------------------------------------
diff --git a/ApplicationLibCode/ProjectDataModel/Polygons/RimPolygonFile.h b/ApplicationLibCode/ProjectDataModel/Polygons/RimPolygonFile.h
index d452b453ab..abb3568c05 100644
--- a/ApplicationLibCode/ProjectDataModel/Polygons/RimPolygonFile.h
+++ b/ApplicationLibCode/ProjectDataModel/Polygons/RimPolygonFile.h
@@ -34,14 +34,14 @@ public:
 
     void setFileName( const QString& fileName );
 
-    void loadData();
+    void loadData() override;
 
     std::vector<RimPolygon*> polygons() const;
 
     QString name() const;
 
     // A file is a leaf folder. Refuse to grow sub-folders inside it.
-    bool                 canAddSubCollection() const override { return false; }
+    bool                 canAddSubCollection() const override;
     RimPolygonContainer* addNewSubCollection() override;
 
 protected:
diff --git a/ApplicationLibCode/ProjectDataModel/Polygons/RimPolygonInView.cpp b/ApplicationLibCode/ProjectDataModel/Polygons/RimPolygonInView.cpp
index c7e7774e66..687be4d8f6 100644
--- a/ApplicationLibCode/ProjectDataModel/Polygons/RimPolygonInView.cpp
+++ b/ApplicationLibCode/ProjectDataModel/Polygons/RimPolygonInView.cpp
@@ -82,6 +82,14 @@ RimPolygon* RimPolygonInView::polygon() const
     return m_polygon();
 }
 
+//--------------------------------------------------------------------------------------------------
+///
+//--------------------------------------------------------------------------------------------------
+RimPolygon* RimPolygonInView::sourceItem() const
+{
+    return polygon();
+}
+
 //--------------------------------------------------------------------------------------------------
 ///
 //--------------------------------------------------------------------------------------------------
diff --git a/ApplicationLibCode/ProjectDataModel/Polygons/RimPolygonInView.h b/ApplicationLibCode/ProjectDataModel/Polygons/RimPolygonInView.h
index 002c2c3f5f..ffcfbb14fd 100644
--- a/ApplicationLibCode/ProjectDataModel/Polygons/RimPolygonInView.h
+++ b/ApplicationLibCode/ProjectDataModel/Polygons/RimPolygonInView.h
@@ -52,7 +52,7 @@ public:
     RimPolygonInView();
 
     RimPolygon* polygon() const;
-    RimPolygon* sourceItem() const { return polygon(); }
+    RimPolygon* sourceItem() const;
     void        setPolygon( RimPolygon* polygon );
     void        updateTargetsFromPolygon();
 
diff --git a/ApplicationLibCode/ProjectDataModelCommands/RimcNestedCollectionBase.cpp b/ApplicationLibCode/ProjectDataModelCommands/RimcNestedCollectionBase.cpp
index 34cfd6a5a2..71fea0adb5 100644
--- a/ApplicationLibCode/ProjectDataModelCommands/RimcNestedCollectionBase.cpp
+++ b/ApplicationLibCode/ProjectDataModelCommands/RimcNestedCollectionBase.cpp
@@ -42,13 +42,13 @@ std::expected<caf::PdmObjectHandle*, QString> RimcNestedCollectionBase::execute(
     auto* coll = self<caf::PdmNestedCollectionBase>();
     if ( !coll || !coll->canAddSubCollection() )
     {
-        return std::unexpected<QString>( QString( "Cannot add subfolder" ) );
+        return std::unexpected( "Cannot add subfolder" );
     }
 
     caf::PdmObject* added = coll->addNewSubCollection();
     if ( !added )
     {
-        return std::unexpected<QString>( QString( "Failed to add subfolder" ) );
+        return std::unexpected( "Failed to add subfolder" );
     }
 
     if ( auto* asNested = dynamic_cast<caf::PdmNestedCollectionBase*>( added ) )