We have to keep in mind that 99% of the folks who create and write these laws are probably not boaters themselves, and because we have a democracy it means that an awful lot of elected folks have no real expertise in what they're doing. Unintended consequences are part of a democracy which we have to put up with to gain the other advantages of a representative form of government. Layer our federal system on top, with 50 different states and 50 different sets of laws, and it is a wonder that we can function!
Just for example, New York, where I currrently live, just passed a sweeping gun safety law that does among other things limit the number of bullets allowed in a magazine to seven, but they forgot to make an exception for law enforcement. So, all of a sudden, theoretically every law enforcement officer's sidearm is illegal. I understand that this week or soon they are going to quietly pass a clean up bill to fix this and other mistakes made in the law.
In Florida, I strongly suspect that most officers finding you without a state registration would simply give you a warning and let you proceed on. I think the infamous Venice Water Nazi gave people two weeks to get it fixed. Not ideal, but I have always found if you act courteously, have as many ducks in a row as you can, and don't get angry--just stay persistent--you can usually overcome most bureaucratic snafus. I had to battle with the authorities in Isla Mujeres to let me out of Mexico because it turned out when I checked into the country somewhere else the local guy didn't have me fill out the correct paperwork. I finally ended up in the port captain's office, or whomever the head cheese was, and eventually he closed the door and told me that I was in violation of all sorts of laws but since all I wanted to do was get permission to leave he would grant me my exit papers. It helped that I had my 11-year old Spanish speaking daughter with me. Out came a big stamp and boom, boom, boom everything was made good and away I went.