Hmmm... strange. I wonder why the ID's changed
Ok I just had a look and you're right, and I've just worked out why... it looks like when the users were imported to the new forum (4.0.1) it only imported active accounts (not the deleted ones) and renumbered them all over again.
Wonder if there is a way to get it to recount the members in the 3.8 database... I might have to enquire about that on the official forums.
Thanks for pointing me in the right direction Xanlamin