I don't care about Yamaha 125s either.
I think you will find YZ125C was '75 in Australia , NZ, SA and Europe while in the US they are 1976 models.
Much the same as YZ250/360B is a '74 model in Australia & Europe while it is a '75 model in the US.
My brother owned a YZ125C in very early 1975 (the second one in our club at the time) because it was so much faster than the RM125 (which was quickly replaced by the much faster RM125S). The YZ125X was available very late '75 ('76 model year) in Australia and then replaced by YZ125D in late '76 which was the '77 model.
I am sure you know better so I'll leave it at that.