I had to call AA a few times in a similar situation. It's really unfortunate that it takes HUCA for AA, the ticketing carrier & also itinerary holder, to assign a seat. I recently booked a AA-marketed JL-oprated flights via a travel agent (AMEX), and assigning a seat was a piece of cake for the travel agent I wonder if it's that many AA agents simply don't know the trick to assign seats for code share flights or don't even have authority to do so.