Originally Posted by HaloTitan
I haven't heard anything about this being glitched. I've played the game all week from start to finish and I got that one in the middle. Heck, I still have one last achievement to go through and that requires another playthrough (ranked). I wish I could help you out, but all is working well on my end.
My guess is he just hasn't played it long enough. Not sure if ranked mode counts towards this either, but I am pretty sure it does.
EDIT: I just checked his gamercard and he has the full 1000, so it was just an underestimate on his part.