Of course the first point does not differ from what others have stated, i.e., there is NO seat selection prior to 24h of the flight for non-elites. What I found interesting was how it worked.

1. Bought TKT on AA.COM, AA codeshare of IB operated flights RT JFK-MAD
2. Could not select seats on AA.COM
3. Went to IBERIA.COM, record locator not recognized.
4. Proceeded thru phone contacts and various hassles described by others previous posters, problems with the 5 digit booking code....
5. 24H prior to flight, went to online check-in on AA.COM, fully expected it NOT to work, but it did, and I got an aisle seat in the center section of the A340, ended up with empty seat next to me.
6. On the return, 24H prior to flight AA.COM indicates they cannot check me in, go to IBERIA.COM.
7. NOW THE AA.COM record locator IS recognized by IBERIA.COM, I select a similar seat and had no one next to me on the return.

What is most odd to me is that the same record locator is NOT recognized by IBERIA.COM initially, but by the return flight it was. Oh well, the situation was not nearly so bad as I expected it to be. Of course, I was a solo traveler, but I did see many rows of 4 with NO seats selected at both check-ins.

Anyway, my two cents and this was just this past weekend.