Not true. I went to Bimini on a liveaboard, the captain had a list of them. I seen myself having them arrive, find it, dock. However, as I seen, some were found to be missing and they had to drop an anchor. They said, fishermen cut the buoys, for whatever reason. Also, a lot of moorings are done badly and they simply break, replacing one is costly and done usually by charters that need them. Once they replace it, they are very possessive about it. Most cost comes from buying an underwater drill that is $10K+.
As I seen at Turks and Caicos, also, some charters would replace or place a mooring, later if they will find someone docked at it, they ask them to leave asap. Thus, competing charters would have to install their own mooring near a popular spot so they could peacefully coexist.
Try calling juliet sailing in miami (julietsailinganddiving.com), they surely would know. If they will share, I don't know. Seems like this info is proprietary with scuba charters.