It's a common misconception. Actually...NORINCO didn't manufacture any SKS.
NORINCO primarly exported the milspec SKS type56 and the commercial variants. After 1980-- when Norinco took over operations at the former arsenal /26\ aka Jianshe-- the rifles they "made" were already made or merely assembled from large caches of parts and components accumlated from the three decades of SKS production in China.
Amending previous reply to consider the possibility that NORINCO might have played some role in the partial manufacture or design of some of the very late commercially modified variants-- such as those models which included parts or systems that were not part of the standard mil-spec design-- like the shortened gas tubes, and AK mag wells.