Last time I called to complain about the lack of upgrades forthcoming, the MP rep said that 1K's were entitled to 1 "set" of confirmed upgrades every quarter in which their total travel exceeded 10,000 miles.
It was unclear how many confirmed upgrades comprised a "set," but she did say that you should get one in a quarter, regardless of how many miles over 10,000 you earned - that the mechanism was unlike the OW UG KIT coupons.
Call another person, get another answer. Keep trying until you hear the answer you like.
Greg