Eh? AA reservations won't make you a reservation? What exactly is AA reservations for then?
If the flight is on some other carrier and you know that carrier's underlying PNR then just call that carrier's reservations and change your booking. If it's on AA then just call the Plat desk again until you get an agent who has a clue.
DONE3 are not "VALID FLT/DATE SHOWN" so the date on the ticket coupon doesn't have to match the date on the reservation.