I'm not quite sure how you got information on how many open guarantee spots there are. They don't even release such info on the booking engine. If someone at the cruiseline said there are 53 guarantees, be careful, that's probably how many have been booked in that category and not how many are left. The guarantee promos are subject to change at any time and often do. The best bet is always to book as soon as you've idintified what ship and sailing date you want. That way if rates climb, and many have been climbing last minute instead of falling as they have at times in the past, you're protected. With RCI there is no down side to booking it early. If they do drop rates, even after penalty and full payment, they'll adjust the rate to the new lower rate for you.