It is probably a K Yairi instead of an M Yairi. The YC models are sold outside
of the US by the K Yairi side of Kauzo Yairi's companies. It may have an angel
burned into the heel block. It is not the Alvarez Yairi brand which is sold in
the US.
Beyond that, I can't tell you much. It is probably as nice as you say. Those
years produced a lot of nice Yairi classicals.
Mark