I've seen a variety of Norinco rifles at M14 tuning clinics. The mainstream batches seem to have gradually improved in quality. The earliest M14 I've seen had a beautiful deep blued finish, with the Star-Trek Norinco logo on the left wall in place of the telescope base lugs, and a USGI walnut stock. There have been a variety of internal differences on the trigger groups, and there are grind marks on SOME receivers where the full auto lug MIGHT HAVE BEEN. I've seen various combinations of stocks, bayonet lugs (on or off), spongy to marginal back sights, welded (or not) flash eliminators and location of engravings/serial numbers.
In short, the later ones are probably better than earlier ones. We are told by the importers that these rifles have been assembled from parts. There may have been some short production runs to make up for shortages, but supposedly there plants making them any more.