Currently, the update of an existing document in the copied process will overwrite the document in its parent process. User has no idea what is behind the scene thus it will be beneficial to prompt a message before the document in the copied process being updated or replaced.
Regarding documents in historical versions - this can be tricky as it's possible that one version of a process can have multiple versions of a document so which version to show? Right now every document change is captured in the change log so it's possible to find out which from the document history. However some UI changes could be placed on historical versions to inform users of multiple versions of documents. We don't have this planned right now but we'll gauge interest in this idea from other customers.
Thanks again for contacting us.