Wondering if someone has a rational explanation to this…

Booked round trip flight through Amex Travel using International Airline Program, CLT-ORD-DUB on Oct 2 and DUB-ORD-CLT on Oct 15. All flights operated by American Airlines, flight sold by Iberia - Premium economy on the international segments only.

Flight confirmation from Amex showed two PNRs; the first (AA) allowed me to reserve seats on the CLT-ORD segment, but not the other three. The second seemed to be an Iberia PNR, with same information - no ability to reserve seats due to flying on AA metal.

After multiple calls between Amex and AA, turns out there’s a third PNR (AA) that shows segments 2-4 only - and allowed seat reservations on those segments.

Should I be concerned about the split PNRs? I now have seat reservations on all segments, but the first PNR has conflicting seat data to the third one for the ORD-DUB segment - system-assigned economy seats on the first PNR and premium economy seats (my choice) on the third PNR.

Huge thanks in advance if anyone can explain what’s going on, my head is spinning!!