AA's seat preview and Seatguru both show Row 29 as MCE on 772_v2 and not on 772_v1. Why are you certain there wasn't an equipment change from what was originally loaded in the reservation system?

What day did you fly? (assuming it was AA314, 6pm, the only MIA-LAX on a 777). Was your Row 22 seat right in front of the lav, with only 22A and B, no seats C through L in row 22?

From the flightradar24 tail numbers and this 772 upgrade status, the last 4 days had configurations with Premium Economy, meaning 29 is an MCE seat. (4 have BEA seats, 2 have Zodiac seats, but all are PE upgraded)

(Updated - read the table incorrectly)