Import marks... What does that do to the value?

[Vlim]

I think the current visible markings are the result of tightened 2002 ATF rules:

Similarly, firearms and large capacity ammunition feeding devices which contain required markings obstructed in whole or in part from plain view must be remarked with required markings that satisfy the conspicuousness requirements described above. For example, required markings may not be placed on a portion of the barrel where the markings would be wholly or partially obstructed from view by another part of the firearm, such as a flash suppressor or bayonet mount.