Prior to 2002, there was a fair bit of cross border trading among firearms owners. That is one possible reason why your SKS bears US importation stamps.
The Russian SKS's brought in by Century were most likely from Syria. Many of the stocks had minor repairs done to them, often with beech wood, at the heel and toe. It looked like the armourers had British training, as the repairs were identical to those done to Lee-Enfields.
The quality of any and all military surplussed rifles range from night to day. Many have been rearsenaled, used and abused. Never mind the "home gunsmithing" that occurs in the hands of civilians. Just recall the wonderful M-1 Garands that came to Canada via Vietnam. Most should have been scrapped. All the Chinese Type 56 carbines that I've owned functioned flawlessly, and grouped 6" or less at 100m, according to Soviet military standards. There is no difference in quality between a screwed barrel or a pinned barrel. Millions of Kalashnikovs can't be wrong.
Norinco is North China Arms is Factory 26, etc....It is all owned by the People's Liberation Army.
Unless some miracle happens, I don't foresee the government allowing the mass importation of Soviet-Chinese-Romanian-Albanian-North Korean-Yugo-DDR SKS's any time soon. They've already stopped further importation of deactivated military firearms. Get them while you can, and don't bubba them.