Or guns made before 1968 that weren't serialized (usually inexpensive) and reducing the numbers would be Guns exported (non-Government Sales) and those destroyed...just like percentage numbers thrown out to support an argument, I expect the Government only has a guess based on whatever numbers they could google...Personally, IDGAF how many they think We have, just so long as they don't know how many I have.Or home made modern guns.
An interesting tangent is the History of Bannerman and more so Bannerman's Island where they had so many surplus Guns (barrels) History | Bannerman Castle (might not have the Barrels used as rebar story)