Scrivener by default creates backup copies of the project, and zips them into a single file, every time you close the project. Those should be in your Time Machine as well, though if you’ve never messed with Scrivener’s backup settings, they will be in the old account’s Library folder, under Application Support/Scrivener/Backups.
Time Machine should in theory allocate the file to the user that restores from it, but do make sure you are using the Time Machine interface to do so, not just plugging the drive in and going in directly with Finder. It isn’t recommended to copy files out of it that way (by Apple, that isn’t just a Scrivener thing). You want to navigate to where it is, in Time Machine (with all the stars and sci-fi stuff), and restore it.
See also:
- §5.2.3, Restoring from Backups (there is also a section on Time Machine there).
- A post with tips on comparing projects. Scroll down to the paragraph beginning, “And so to that end…”, as the top part is a response to the feature request itself. I wouldn’t want to go solely by word counts (via
Project ▸ Statistics...) as that could change for a large number of reasons, or even not change for drastic reasons (write 3,000 words, delete 3,000 other words).