If you are Platinum PC, there is the benefit of getting a room with a 72 hours advance reservation even if the IHG hotel is sold out, with few exceptions. You call the PC reservations line. You must pay the prevailing rate. Notable exception would be where the hotel in question has had all its rooms taken over by the government. One such example was here in the US after Hurricane Katrina when FEMA contracted for all rooms in certain hotels to house evacuees.

If, in addition to being Platinum PC, you are a Royal Ambassador, this benefit is available for IC hotels with but 24 hours advance reservation by contacting the Amassador reservations number. To be "guaranteed" you must call before noon local time the day before arrival at the intended property.