Anybody know?
google halo 3 stats and click on the link for the halowaypoint site. It will bring up the halo 3 stat tracker, they no longer update it so it is your pre existing stats just so you know.
You mean the bungie website, not waypoint.
Anyways, here on waypoint, click on “career” above and to the right of this page, and then go to “waypoint career”.
Scroll all the way down to where the Halo games stats are and press on the arrow to continue and Halo 3 is there.
^ that AND the stats DO update.
On Bungie.net they don’t, since the servers migrated to 343.
But here they do, sure. 
They’re rather incomplete, that’s a whole other story. 