I experience something similar the other day when I logged into Halo 4 for the first time this October. I logged into the game and immediately got 13 or so achievements for 300 gamerscore. I thought it might be because of an update and these were achievements I had previously gotten outside of DLC's that would now be awarded to me or something. But after going through them I realized they were every single achievement from Crimson and Castle DLC's (that I didn't previously have), but not a single one from Majestic.
So, kinda confused on this. I did buy Majestic when I bought the Season Pass and got the other two, but perhaps it didn't download properly or something. I'll check on that, but I just thought I'd throw out my experience with this because I am still a little unsure.
