basically.. in the forum, you can see when it's been edited (last?), but in the game page (userdata.php) it only shows the timestamp of the original post..
yes, it works that way. Nothing I can do about it, it's the way SMF works.
you might want to make separate announcements instead of editing existing post (or add your own time stamp)
wonder how a follow-up post in the same thread would work?