Only selective CX fares (i.e. the higher and more expensive ones) earn AA miles. Double check the rules for CX miles credited to partners from CX/AA sites. I suspect your missing CX flight was illegible for AA credit.

For more specifics about CX, you should check out our Cathay Pacific Asia Miles Forum.

Even when you are forced to redeem for "lifestyle awards", at least being HK-based, your options are wider and better than those of us Taiwan-based.