If the AAA discount rate is not out at the time I book, I book at rack rate to hold the room. When the AAA rates come out, I check frequently and modify my booked rate to the AAA one.
It is not automatic. You have to call reservations and request your rate be modified.
came back to say, I don't know if you can book 20 months out.
Make sure you book directly through the Loews website or call them. This makes it a lot easier to just call again when rates go lower and have it changed without penalty.