Originally Posted by surryson

For points to be absolutely sure to credit to your preferred FF scheme, an agent needs to delete the old number from the PNR and add the new one into the PNR.
If a change is done by a check in agent, lounge or gate agent, there is no guarantee that a change made in the DCS system, FLY, CM etc will stick.

Data points so far:

BA in the PNR. CX flight. Change to QR at check in. Credited to QR.

BA in the PNR. QR flight. Change to QR via live chat. Credited to QR.

BA in the PNR. BA flight. Change to QR in the CCR LHR. Credited to BA

BA in the PNR. BA flight. Change to QR by reservation trained agent on the Gold line. Credited to QR.

BA in the PNR. BA flight. Change to QR by reservation trained agent at the First Wing. Credited to QR.