I was told by the manager at CBR that requests that are on the reservation when you first book it, is what they go by and then when you actually check-in, you are given the requests as long as they are available. Your first request is the main thing they go with, and if they can accommodate the other requests you may have they will. So if tons of people are requesting Martinique, the first ones that arrive at check-in get the requests. This happened to me the first time I went to CBR, I arrived and got to the checkin window by noon, but Trinidad North (my first request) and Martinique were already full, so I got Jamaica, which turned out to be so wonderful that it is my first choice now.