Yes, IIRC firearms prior to the GCA of 68...? Were not required to be import stamped....
Some folks appreciate rifles/handguns that do not have import marks. Those folks don't mind paying a premium for lack of import marks. Some folks only collect guns with the small import marks on the barrel. I just about refuse to buy guns with the huge billboard import stamps(capture/recapture are exceptions...)....really disappointing. I have been lucky collecting and have found a number of firearms with no import stamps.
Soldier bringbacks are another exception, although without proper documentation, one cannot prove provenance.
Pahtu.