The text in the offer says:
Simply register prior to travel using promotion code NAF15, purchase a qualifying First Class, Business Class or select Economy Class fare ticket* and complete travel by January 31, 2016.
The conditions just say:
Registration prior to travel is required using Promotion Code NAF15 at www.aa.com/offers.
So, who knows what will happen. But you have nothing to lose by registering and AA has done it differently before.