hhoope01

If Starwood's system is anything like Marriott's, changing a check-in date essentially means a new reservation is required. They can change a check-out date without creating a new reservation, but not the check-in date.

So if the hotel really is sold out for some of the nights, then someone at the hotel may be required to make a change to the check-in date (assuming the hotel staff is willing to make that kind of change.)