The reason for treating European PLUS as C (also on revenue tickets), is likely the same as the award pricing. SK would otherwise not be able to offer lounge access in PLUS almost anywhere. From what I know *A does not recognize that economy premium exists also in the revenue tickets. This is also likely because there is no uniform standard expectations for Y+. SK decided to drop C, in favor of Y+ many years ago. LO, I believe, not so long ago, dropped Y+ in favor of C. There seems to be little market for a Y+ product without lounge access (basically a Y product plus food on board).