I've cancelled once or twice inside the window, but in those cases, when I called Plat Concierge I volunteered information about where I was stuck or the number of my cancelled flight. At the same time, I asked them to book me into another Starwood property in a different city or at the airport where I was stranded. Thus my reasons for requesting a late cancellation were pretty clear and could have been checked easily. I never had a problem with being charged by the hotel for the reservation that I coudln't use.