This article is from the Yashica SLR FAQ, by email@example.com (Cees de Groot) with numerous contributions by others.
Yashica DSB lenses are single coated, ML lenses are multi coated (ML
stands for Multi Layer). As usual, a marketing department messed
things thoroughly up by introducing another designator, MC for Multi
Coated, for later multi coated lenses. Contrary to the quality jump
from DSB to ML, there is no distinguishable quality difference between
ML and MC lenses. For quite some time, Yashica offered both DSB and ML
lenses; later on, DSB lenses were sold in package deals with bodies
(like the FX-D Quartz SE and the FX-7).