Any Yashica ML expert?

[Lucio]

I just bought a 28/2.8 which is a pretty good performer (except for flare resistance) and I'm curious to find out if that's the first version (8 elements) or the second one, that is supposed to be better (7 elements).
SN is A12051951. I also tested a few copies with SN over A124XXXXX and they were all a bit worse, but not by far.

I'm also curious about the meaning of the three letters on the bayonet of some of those lenses: PDO, KJO, NJU...

Finally, I noticed that the some lenses have a three screws bayonet and some have a 4 screws bayonet, but that seems unrelated to the progression of the serial numbers, like some lenses were manufactured in some factory and some lenses in another one, during the same time (maybe that's what the three letters are indicating?). And that's true for the 28mm just like for the 24mm (I'll test a few copies of the ML 24/2.8 in the next few days). Maybe that's a coincidence, but the copies of the 28 with 4 screws were better, as far as alignment is concerned.