There are variations in all older lenses. I've had a few different Yashinons, Xenars, Tessars, Rokkors- lots of variation in the quality of the lenses.
Coating technology was changing constantly throught the late '50s and '60s. I assume that Yashica for the Yashinons just went with whatever the rest of the optical line was using that month/year/decade.
And then you add in the variations of shutters, lens boards alignments, etc.
The sharpest Tessar-type lens I've had was a Xenar on a Rolleiflex. Then a mid-run Rokkor, then a mid-run Yashinon, then a pre-WWII uncoated Tessar. Go figure....
Considering the number of Yashica-Mats made over the years, and that Yashica was not aiming for the highest quality (cf. Linhof selecting Schneider or Zeiss samples for its cameras), sample variation is probably more than most other quality TLRs.