What kind of reach beta? Seeing as the game has gone gold I wouldn't think there'd me any multi-beta, and single player I thought they kept close to their chests...
idk i still have the codes and havent used them since they came out due to me not playing xbox anymore
With reach if you have the version you downloaded with a code and not with ODST you can still load it up and watch replays, thats all you can do though.