We're excited to announce that we've fully migrated the Xbox Forums to their new home, here on the Microsoft Community forums!
As of today, going to forums.xbox.com will redirect you here to the Xbox area of the Community forums. We've moved all of your existing threads over so you can continue and start conversations with the new forums experience.
We sincerely appreciate the feedback you have provided over this transition and can't wait for you to check out the new Xbox Forums!
It tends to mean they haven't been online in a while, rather than saying Last Seen 467 days ago (perhaps a slightly extreme example). I don't think it has a specific cut off point, everyone seems to get reset to that occaisionally (assumedly when they run
maintanence on the servers) and so it stays like that until they next log on.