Like mentioned above, every state is different, here in NJ, they wouldn't accept an expired PA registration as proof of ownership even with a notarized bill of sale.
The boat had been unregistered for 20 years and still owned by the original owner. The PA registration had an ownership transfer section on the back. NJ wanted the original PA owner to supply a current registration, PA wanted that owner to pay up all the previous years registration to get a current reg. card. It took 3 months and a court order to get it registered and titled in NJ. The seller hadn't touched the boat in decades, they only sold it to get it out of the yard. The amount to pay up the registration fees was more than the boat was worth.
In NJ, they have a procedure but it opens you up to just about anyone laying claim to the boat in question. You basically have to post a letter of intent in the local newspaper announcing that you have a boat with no proof of ownership and that if anyone cares to lay claim to it, they must do so immediately.
I've been trying to register a boat which I myself bought brand new back in 1978, prior to all the current laws, the boat sat unused in the garage for 35 years, now they won't let me register it because I don't have sufficient proof of ownership, which means either a certificate of origin or current registration for that size boat.
When I bought the boat, all I got with it was a cash register receipt from the sporting goods store where I bought it.
So now it sits in the back yard upside down useless because all the ads and fees needed to file for proof of ownership here far exceed the value of the boat.