IF your reasoning would be correct, CX could just have stated with the conditions: "Only those flights, illegible for earning miles with AM or flights redeemed through AM".

Which CX did not do, on the contrary CX did specify, staff and prize tickets don't apply, as well some code-share flights don't apply. That's it.

Of course, this is CX and the world could be different, and the conditions are just badly worded, though for now, there are no reasons to assume so.

What seems to be important is, one registers its CX FF number with the flight, before boarding, which suggests, a claim afterwards, might be rejected for MPC status extension.