No HIN visible on 1973 20'

[Dolphinfish]

I am looking at purchasing a 1973 20' that has been redone - new deck, fuel tank, wiring, etc. This rebuild is well documented with photos and is well done. The problem is that the person who did all the aforementioned rebuild did not do the transom but merely painted it with the hull. There is no hull ID number visible. He said that when he bought if from the prior owner in Miami it had no number visible at that time (2013). Who knows how many people have refinished that hull over the years. I asked if he had any trouble with the title transfer and registration and he said, "No, I walked in with my Bill of Sale and old title and they issued me a new one in my name." Since I know of know way to otherwise reconstruct or determine the hull ID on this boat, should I be concerned or is this a rather common issue on a 44 year old boat?