They are updated via build_userstats() in functions_databuild.php IIRC, if the datastore is corrupt and you view forumhome or login to the ACP it re-builts it I think, also upon new registations it should.
Well it stayed with the same user for days, after 3 new members later, it updated. Also whilst i got this post, my email isnt working on my site to me, as in getting email replys etc. But it works fine for every other member