I'm guessing that the "edited by" attribute of the post is contained in a different table than the posts that were lost, probably specifically referencing the post number. Since the posts were deleted, the main post database is probably reusing old post numbers, cross referencing them to the "edited by" table, and coming up with bizarre erroneous matches from last year's edits...
Which means there's a year or so left before the problem resolves itself unless someone fixes it by clearing / editing the old "edited by" list which is essentially corrupt past the date of the last saved post from the crash.
Then again, they might store it in the user information, forum software usually contains all kinds of levels of gayness retained from the early versions and it's hard to say how they would have programmed it.
... but apparently new edits are being added correctly. I wonder what happens if you try to edit a post that's showing the edited by message?