There is no Yk1... there are S1, A1, Y1, J1 and YS1 cable B-series trannies. YS1 is strictly a 92-93 code, so it must have been a replacement tranny for that 90/91 car you saw.

I do agree with you about the prevalence of non-GSR YS1 transmissions. A friend of mine told me he got a GSR YS1... based only on the YS1 sticker on the case. It was apparent that it wasn't a GSR as soon as I drove it.