They are referring to the date code and the 15 round magazine. It is prior to the “Federal Assault Weapons Ban” of 1994 to 2004. https://en.m.wikipedia.org/wiki/Fede...lt_Weapons_Ban
If you had a Pre Ban you could keep it or sell it. During the ban, only law enforcement and military could purchase high cap magazines manufactured at that time. Also, high capacity magazines manufactured at that time were supposed to have the Law/Military warning stamped on them.