Unnecessary as the AA PNR works just as well (they either both work, or neither
).
Cheers.
They do but I have found the following exception:
I flew SAN-LAX-LHR-TXL-LHR-LAX-SAN (whole itinerary on one AA PNR, one ticket) with the flights btwn LHR-TXL on BA.
LHR-TXL was tickted as AA codeshare, TXL-LHR as BA flight
I this case, mix and match of BA flight and AA codeshare for BA metal flights,
my AA PNR didn't work on BA.com. I called AA and it turned out that I had
two different BA record locators. So I had to go twice to MMB on BA.com for each BA PNR to be able to select my seats.