You have NATO over-stock. Winchester is simply selling off their over-stock and you have the mixed production. Nothing wrong at all.
OMG! That is it! During shipping, the brass gets "polished" by the jostling of the movement. Can't believe I didn't see that... Great post!Take a look at the rounds in the styrofoam block and see if the discoloration ring doesn't match the depth the rounds are seated into the block. I think that's the discoloration story.