since I changed my Gamer tag, now when I click on service record for past halo games, it says no information available, how can I sync my previous stats?
It may just be an error in time, depending on how long ago you changed your GT, it may not have registered the change fully yet. That is one of my guesses on it, at least.
Playing a game or two on Halo 4 will update your service record.
Hi Arkantos Drakon,
Only Halo: Reach, Halo 4, Halo: Anniversary and Halo: Spartan Assault stats will carry over after you’ve changed your gamertag. You may need to complete a match online with the new gamertag for the stats to populate again.