Frankie,
While playing Halo: Reach this week I had the “Both Barrels” achievement pop up. The thing is I do not have any of the DLC map packs nor have I ever played on them.
I’m absolutely gutted, I have OCD and have been quietly working away at Reach, since September last year, to get it to 1000 and that’s what I consider complete.
Is this a glitch?
After googling the issue I discovered several threads in various forums with people saying they had unlocked achievements without owning the map packs. The suggestion is that it was caused by the title update.
I’d really like to know why was nothing mentioned?
I really hope this isn’t a ploy to get people to buy the Map Packs (because I assume completion can only be reached by purchasing the map packs).
IS THERE ANY WAY I CAN GET THE ACHIEVEMENT DELETED?
What is going to happen with this (which achievements are now unlocked for people without he map pack, will it be fixed so that only players with the packs can earn them)?
I know this isn’t a big deal for most people (and I’m well aware of all the “real” problems in the world) but I have a real thing with numbers which I can’t help 
Any official response will be greatly appreciated
Thank you