Even though your achievements are tied to your GamerTag .. you do not have to be online for them to update to your 360.
For example, if you had played only King Kong all the way through, your GamerTag on your 360 would show all the achievement you had completed and would show a Game Score of 1,000. Once you hook up to Xbox Live, this information is pushed out to the servers so that your online profile reflects the information that is stored for achievements on your 360.
If the OP did actually complete the achievements, he should have still seen the information reflected on his GamerScore on HIS 360 as soon as the achievement was complete.
I was simply stating, since he said he was signed into Live, that if he was playing the game on Live with another user, he would not earn the achievements (since the description of ones like Complete a Game, Score a Touchdown, Get a First Down) all require that you get those in an OFFLINE game.