Answer
A workable pattern for this kind of creation-source branching: use a script task to classify the incoming data into a status-style variable (like "Copy" or "Reference"), then route through a gateway condition checking that variable — one branch going to the IFS Failure End Event (when the scenario truly can't be handled, like a missing back-reference) and the other continuing to a normal end event. Debug the workflow and step through both variable values to confirm each path resolves to the branch you expect using the workflow's inspection/eye-icon view before relying on it in production, since getting the classification logic exactly right for your specific scenario may take some iteration.