No it's happened to me a few times, I've had 6,303 (I knew 'cause of a .303 calibre rifle, numbers with meaning are good) and then when I came back on after a couple hours, I had lost about 5 posts.... no idea why, it's very weird.
If threads get deleted do we lose the posts from there, thus losing post count? As if we still had those posts, they'd be on the members list, under "3 sheets' posts" and as the thread isn't there anymore, then the thread can't be... it sucks! lol