I would not even bother with AA or the CX website and just call CX directly. In my case, we wanted 1A and 2A in the 777. 2A showed as unavailable on the CX website, and AA said it was blocked.
CX was able to unblock it and gave us what we wanted in a 2 minute call. But it did take about 20 tries as I kept getting a busy signal on the CX 800 number.