I discovered a little quirk a few years ago trying to book a government campground out west. All the sites were unavailable, apparently fully booked, I assumed, which didn't make sense to me since the date was off season, and way in advance.
Finally I learned they showed it that way after Labor Day because they did not bother with reservations, yet the campground was still open for whoever showed up to check in with the host, Which we and others did, selecting whichever site we preferred. The rangers had closed one section, but the other was up and running.
Not saying this is your scenario or that Florida does it that way, just that sometimes the system may be hard to decipher.