I tried a booking for Athens IC that was sold out in October 05 and I called PC/Ambassador service center about guaranteed booking. They told me the property was booked due to a convention, but offerred to put me on a wait list. I did even though I though it would be a waste of effort, but three days later they called me back and booked the room.

I do know that IC's will overbook - perhaps as cancellations occur and they become less overbooked they will allow more bookings. ^