Originally Posted by
USFlyerUS
There's a thread somewhere about the misnomer of "linking". From what I recall, the "linking" is merely entering the other PNR # into a free form field. The PNRs are otherwise not really attached together in the way I think you're thinking.
Correct. It's not possible to link two PNRs in the way OP wanted to do it. Tickets must be booked together to be put on one PNR. You will always be on separate PNRs - which can never be combined - if you book the tix separately.
Probably also a mistake to ask an AA gate agent to fix the seating arrangements. You might get lucky but it's equally likely you'll get an unhelpful response. Better to just trade on board as OP did for the first flight.