I was not aware of this grandfather clause. I think David has it right. I asked the harbor master, and here is what he said:
With the economy, things are moving on the waitlists, but it is a crystal ball question to predict when someone may come up. As to the situation that you described, the folks advertising on Craig’s List are in error. They are annual transient and the slip does not go with the sale of the boat. He has a year to put a new boat in a slip for himself. It is my intention to end the “grandfather” situation that allows even the year.