Is the paint still bonded to the wood? If so, it would seem that roughing up the paint enough to provide a somewhat fresh and abraded surface would allow new paint to stick. Once you start sanding you can spend lots of money, time, and effort to achieve some form of perfection. Don't ask me how I know.
If the task at hand is to protect the wood underneath with a fresh coat of paint before winter sets in do enough to bond the new paint. Just my two cents, take the advice for what you paid for it!
I agree with Rick. If the paint is still bonded to the wood, I don't see any reason to sand through that bond and try to build a new bond. If you're Type A and desire perfection, this is still an opportunity to move in that direction.
I'm fully Type B, but I am also one who loves a beautifully finished boat. Don't sand it just to sand it, but do sand through a lot of the old paint and use it to fair the boat. Layers of paint will have filled low areas and you can sand off the high spots. Stop when you generally get to the original paint/primer and fill any remaining low spots.