Interestingly, I recently flew YVR-ORD-LHR-ARN with the YVR-ORD leg on AA and the others on BA metal (all on an AA ticket), having qualified as Gold on the outbound trip.
OLCI was unavailable so checked in at the desks in Vancouver and the boarding passes printed off for me showed different status levels (OW Sapphire on one and OW Emerald on the other two).
Not an issues since we were booked in F/J but still an oddity!