Noticing the cut in the bayo lug was missing on MrLC's is what got me to wondering myself....that is when I noticed the difference in my rear sight base too...granted its apples to
Mandarin oranges between my /206\ and these. My lug is like this one, but my sight base does have the cut....whereas this one does not. The differences between this and my 10m and 9m are substantial. I need to hunt down my own 11m now.
I wouldn't be surprised if some parts were manufactured elsewhere and used up at random...by random factories...hence the differences from gun to gun, one would also think while not giving an exact timeline, that it would get you into a ballpark idea of when a particular rifle was made. I don't see them hanging onto N.O.S. for a long time...while tooling may have been moved around somewhat, I suspect that is less likely and modernization practices probably proliferated at a reasonable rate.
What is neat about these bringbacks, especially the papered ones, is that it gives a definitive timeline when the evolution of the Chinese SKS can be solidified...at least to the consistency of a Jello-Shot.
Once the data from other factories can be accumulated perhaps it could 'shed some new light'