I discovered a pristine backup of the original boards as they were originally provided to me, and switched to our original(ish) forum software to merge everything back together. What we had in the archive has been through a few conversions, so some avatars and attachments and stuff had been lost across the years, on top of formatting issues on super old posts. That's why we were on the other software, as a "fresh start" while we worked to find a way to restore the original posts to pristine condition. I was going to come at that another way, but this works too
The version of the boards you remember had to be merged in by hand, so users and posts and stuff were created as and when needed. That's why some recent users have nonsensical join or last seen dates, and that'll get sorted out as I continue to finish things up and bring a few final posts over.