No serial numbers on some of Adam’s gun collection may be due to the fact he collected older and antique firearms. The .22 bolt action rifle my dad gave me as a kid in the late 1950s has no serial number as these were not required on .22 rifles and some shotguns back then. Will the feds call me a felon when they grab mine? Yes, as the agenda is to make all firearms illegal for we civilians.
My model 67 Winchester .22 was bought new in 1940 and has no SN and it wasn’t required unless the firearm was manufactured for export.