^But that's not co-writing either. It's editing. Please stop confusing the issue.
Pardon me for "confusing the issue".
I've done cowriting and I've done editing and they feel quite a bit the same to me. Part of the creative process. Perhaps that's been my problem: too much editing before the first draft is done. But my point is that the collaborative process of writing doesn't have any hard and fast rules. For some writers the steps will blur into each other.
I talked about how Shatner works, and he has mentioned the details of how he collaborates. Whether some bits are writing, some bits are editing, some bits are cowriting, and some bits are transcribing: I don't really care. It's not necessarily going to be easy to define something that everyone does in their own way.