We have documents that may be in the workflow for many months. Sometimes policies change on how they are to be processed. If the policies grandfather the existing documents, then leaving them in the older workflow version is fine. However, the policies may very well dictate that they be moved to the new flow and continue through it. We need to be prepared for that situation so that we can support it.
Could you give me a bit more detail about what the manual migration would entail? Is that something that we would have to write <Java> code to do? Can you easily search the repository for all documents connected to a given workflow instance?