I realize I am just talking to myself, but I am hoping - if nothing else - others may find this process helpful.
Reordering the operations worked as i had hoped, and my suspicion that it would fail if re-run was confirmed as well. It seems all of the .rfa files are being left open in the background of Revit, because neither closing Dynamo, nor closing the Revit file i had open at the time was sufficient. I needed to close all of Revit (which took extra time, since it had to close all of the invisible background documents) before i could run the graph again.
SO, NEW QUESTION - Is there a way to get Dynamo to close all of the background documents in Revit, without closing the active document, let alone Revit or Dynamo?