Boats leave the factory with only a few thru-hulls installed. Then more get added as systems are added to the boat. Generator gets one, AIr Conditioner gets one, water maker gets one, wash down system gets, depth sounder gets one and so on. Of course these add ons are always different and and the thru-hull is always in a different location.
When my boat was being surveyed I mapped out all the penetrations, took me quite some time to identify all the thru-hulls. Many had been decommissioned such as direct discharges for the toilets.