I book us with AA numbers to get preferred seats, then change to AS at the gate for AS earning on the shorter flights where we don't need the AA EQM/EQD.
Last time it ended up crediting to both
Cheers.
CAREFUL: System will automatically move you out of preferred seats if you are not at least MVP, should be okay if you are already checked in, gate agent overrides system.
As SAN has become a focus city for AS, I am able to fly them enough to earn MVP status, find AS miles are worth MUCH more than AA these days...