I've got a flight coming up YVR-LAX 12/02 and returning LAX-YVR 15/02, my first flight on AA so i'll see what happens.
I had a problem adding in my MPC # when buying my ticket, but that was a TA problem, so decided to forget the headache and will just add it at check in.
From the sounds of it most people don't have a problem, so i'm hoping for the best (add to the fact that my new MPC GO card hasn't arrived in the post yet and I'm hoping my 2014 card works)