I disagree with you Robert. The country of origin stamp requirement came into place in the mid 1930's. Most firearms found in the USAthat have it were definitely imported prior to 1968 when the Gun Control Act was passed. At that time with regards to firearms, the country of ORIGIN requirement was changed to country of MANUFACTURE. The rifle in question is very likely as Aussie 48 states, brought back prior to the GCA
'68 and not through commercial channels OR it may have been imported post 1968 and the import marks were not applied. Many thousands of rifles have been imported since 1986 when they started allowing surplus C&R military firearms back into the USA. Warehouse employees are human and it's just common sense that some slipped through the cracks without being so marked.