Don't put to much stock into the guaranteed room availability. The guarantee is that a room will be available if a reservation exists, it does not guarantee that you will be able to make a reservation (like Hilton's). My team and I (all platinum's) were recently denied a reservation at the Calgary Marriott because of a "Blackout Date". The verbage on the reply email they sent me in part is below. Then they recommended that we try one of there competitors. Well guess what for a one week "Blackout Date" we moved our three room reservations from January to February to the Fairmont.

"The guarantee mentioned below is if you did get a platinum override and when you showed up the room was note there."