In my experience, CX releases their awards generally across the board for all its partners. ie when CX sees it, so does everyone else. But once these seats are gone, they're gone. Thats only when having an asiamiles accounts helps as you can waitlist on the flights that no longer have any more award seats. Then asiamiles queues your PNR off to CX inventory control and when they feel like it, a seat (or 2) will be released to the PNR - not to general inventory control.

In this way, CX protects its own members by giving them priority access. Of course having elite status in the Marco Polo Club helps too as preference will be given to those with higher priority status.