I have been told by my TA that the Guaranty rooms are not assigned until the day of sailing, so you could be placed anywhere on the ship.
There is only a certain quota of pre-assigned rooms and once these are gone, you have to accept a Guaranty room in the category you booked.
However, you will always have a slim chance of being upgraded with a Guaranty room. With a pre-assigned room, upgrades just don't happen.