Originally Posted by Mwenenzi

In Star Alliance ff earnings are based on the operating carrier when an eligible marketing carrier (flight number)
In Oneworld Alliance ff earnings are based on the marketing carrier (flight number) when an eligible marketing carrier.
For those revenue based ffp's can be more complicated.

UA is just being a travel agent in selling the last flight. UA & CX are not partners.
Best to credit the CX fight to AA or another OW airline ffp