Highly doubting any data was lost, possibly different number of pages due to all the posts/threads being rebuilt. So if there had been lots of deletions over the years in that thread, the rebuild would have reset the post count for the thread to how many posts actually exist right now, which would in turn change the number of pages. Also, I made several changes last night, mostly server config changes to help with overall speed and such of the site so that should be better now.