Yes. It turned out that NONE of the exported database backups I'd made since the switch to the VPS in 2011 had completed properly, and were unusable. We had to reinstall the old UBB Classic, import the pre-VPS UBB Classic member files, posts etc, then convert it all to UBB Threads and upgrade everything to the latest version of Threads. Then fix it to look like it the rest of the site, since things have changed around in the upgrade (that's ongoing, a few niggles still to iron out).
Let's just say it's been an "interesting" few weeks.
Still - having the first ten years' worth of posts - and the 3,000 members - is better than nothing at all, which is what it was initially looking like. Particularly when there are posts on here from fans and friends that are no longer with us, and so much searchable UV knowledge on here. Very happy we managed to save all of that.