No, one does not have to specifically book a King or 2 Double/Queen room to qualify for the Guarantee. The generic "1 King Or 2 Double" booking that is common at Full Service properties also qualifies for the Guarantee IF your preference of 1 King is set in your profile (which it is) AND your reservation confirmation states that a King bedded room is guaranteed (which is almost always the case for Platinums and would be denoted as K1 on the screen of the check-in agent).