The HIN requirement went into effect on 01NOV72, so any production (or for that matter, "Homemade") boat would not have an original HIN if built prior to that date. Around 1989 or so, many states adopted their own HIN requirements for any boat sold or transferred after a certain date. The State-Issued HINs all started with the 2-letter State Registration abbreviation with the 3rd letter being a "Z", so Massachusetts HINs begin with "MSZ", Rhode Island "RIZ", Washington "WNZ", etc. These HINs were issued to new Home-built boats and also to any boat built before the USCG (National) HIN requirement (1972). If a 1971 built boat has been resold or titled after a certain date (I know it was around 1989 here in Mass) the State would have issued a State-Issued HIN to that boat. So, it is quite common for a production/factory-built boat that was delivered prior to 1972, to now have a State HIN, this does not mean the boat was home built, but only that the boat did not have an original Factory-issued HIN, or that the Factory-issued HIN did not meet the State requirements. (I can't see why any truly Factory-issued and recorded 12-digit HIN would not pass muster, but I have actually heard of boatowners needing to apply for State HINs despite the boat having a prior HIN). I think most Factory built boats (hull and deck) that were finished off by owners ("Kit" boats) would have had a factory HIN assigned if sold after November 1, 1972, but some boat hulls/decks are molded by one company and finished off at another company (custom or limited production models), on these, the company that finished off the boat will usually be the one to assign the HIN with their MIC (Manufacturers ID Code, the first 3 digits of the HIN). So, anyway, a State-Issued HIN does not in itself indicate that the boat was ever titled as "Home Made", but only that the boat may have been built prior to the 1972 HIN requirement. Obviously, just about all Home-Made boats will have State-Issued HINs, but the presence of an "WNZ" HIN does not always indicate Home Made. Some State do however ,list the builder as "Home Made" if the owner doesn't know the builder.
OH, I knew there was another thing that I wanted to mention! Using he sail insignia to ID the boat does have one caveat! Some boats use sails that have been repurposed from another different boat, so double-check before assuming that the sails always indicate the builder/model. On most production boats, the sail insignia will be accurate, but just be aware that used boats sometimes sport used sails made for a different design.