Six DLC achievements ended up glitched after the Champions Bundle came out last year and 343 just releases a fix but I don't think they actually fixed but just unlocked them for everybody. I got all 9 achievements I need to 100% the game and someone on Halo Waypoint got 12 achievements with one of them being a campaign achievement. So if you're curious(As I am) if they just gave all the achievements to everyone and you want a potential easy 2000 GS then you can put in Halo 4.