Well, all that was supposed to disappear was postcount for posts in Talk to the Staff, but apparently someone has deleted a forum or two (maybe Grav?), so posts from those were lost also. I know that we've stopped adding back posts from the pruned trashcan posts for a long time now, so it wouldn't be that.
Edit:
Hmm, actually, the numbers you claim to have lost are inflated, but close to the pruned post count, though I could swear we just left them gone last time