The concept of a HIN, like a VIN, being a long standardized set of numbers and letters establishing manufacturer, model, length, and date of manufacture, didn't exist before 1972. But manufacturers did tend to need to keep track of different hulls to a certain degree. My '69 has the hull number, 112, written in pencil on the inside of some of the cabinetry, but it physically appears on the boat nowhere else that I'm aware.
When I registered the boat in my name in California in 1991, after buying it from the previous owner, it received an official legal HIN that had nothing to do with anything. I subsequently moved the boat across the country and registered it in PA and NY and that number was lost.