Originally Posted by
carlosdca
GENERAL NOTE: If your first leg is on AA (connecting to a BA flight), check-in online at britishairways.com for the BA segment is NOT possible, therefore you will not be able to pre-select seats even 24 hours before departure.. You will be able to change your pre-assigned BA seat at the airport with the AA TA or the BA TA/GA.
Not sure if you mean this to apply just for general members. As a Plat with a first segment on AA that connected to BA, I've been able to choose my seat with an agent, which I then changed on the BA website weeks before the flight.