Personally, given the fact that some Norinco commercial stuff as late as 2018 claimed to be non-corrosive but SOME of it was, I would be leery of any older PRC/Norinco manufactured ammo and automatically presume it is corrosive. I would even go so far as to say it doesn't matter if it's from a spam can or from a factory box.
While the nail test may show that THAT round is corrosive (or not), the amount of inconsistency in the earlier PRC/Norinco rounds would make it difficult to conclusively and comfortably believe that all other rounds of that 2001 years were ok. The 2018 311 18 rounds are a prime example of that. That said, the 311-19 and 311-20 red box rounds have all proven to be non-corrosive.