On an imported rifle, "pre-ban" means "I can prove the rifle was imported before 1990."  Unlike domestic rifles, imports must comply with the '68 Gun Control Act, as modified by the '89 Import Ban, which prohibits "military features."

Note that import guns must ALSO comply with the '94 Krime Bill, just like domestics.

You can change an import rifle's status to "domestic" if you replace enough imported parts with domestic parts, and enough domestic SKS parts are now available.

-Troy