Not sure how long the agreement went, but guns from countries with internationally recognized proof house do not need to undergo re-proof when sold in country that has their own proof house. For example if you find old German shotgun completed in Germany between the wars it will have just Thuringen proof and "not English made" or "not English make" but no Birmingham or London proof, yes? In addition to that guns that are brought in for reason other than commercial sales to the public do not need to go to commercial proof house. Example of those would be West German police guns like the PSP. Modern example would be Soviet Makarov that ended up in West Germany or post unification Germany. Those sold to the public will carry commercial German proof marks those used outside of that purpose will not.
