Missing Achievements.

So, my friend came over and got about 40 gamerpoints on rock band. (He recovered his GT) He went home, and his achievements weren't there. He played GTA 4 and got 20 gamerpoints at his house. We played rock band agiain at my house and he got 25 gp. So now, his profile shows that he has 25 gamerpoints from rock band, and not the 40 from it before or the 20 from GTA 4. Whats going on? Missing Achievements.
are both 360s connected to the internet? if so then idk.Missing Achievements.
Ya they are, but I talked ti microsoft and I figured it out.
I took my 360 over to my friend's house, who doesn't have XBOX LIVE so I couldn't have it either. We played Left 4 Dead and got about 20 achievements. When I came home, I didn't use my XBOX 360 to go online, but i recovered my GT on my dad's XBOX 360. The achievements weren't saved there so I figured it was just because I wasn't signed in XBOX LIVE when I got the achievements but should still have them on my own XBOX 360 since the achievements should be saved to my hard drive. I took my XBOX 360 back over to my friend's house the next day and of course, no XBOX LIVE but my achievements were still saved. When I went home later that day, I was able to sign in to XBOX LIVE but...none of the achievements were there. There is a saved game though. Why am I missing the achievements? (Sorry for keeping it so long but I wanted to be thorough)
Well, I was playing Gears of War and i completed the entire game. I had gotten the achievments required to get the unlockable players on Gears of War 2. However, when I went on multiplayer in Gears of War 2 the game stated i hadn't had the achievments from the earlier version of Gears of War so i couldn't play as the unlockable players and when i checked my system it showed that i had the achievments