Which Jupiter-12 ?

Hello To All,

Would someone please tell me which Jupiter-12 is supposed to have a shorter rear element assembly?
This would be used on a Leica M6 body. I was not aware of one.

Thanks,
Steve

I vaguely remember someone saying something about early Kievs having some kind of depth issue for the J-12 and had their own variation of early J-12s for them? I don't remember where I read it and it's only just from some fleeting mention I saw somewhere, not sure if it's even true but thought I'd mention it at least, maybe it rings a bell for someone...

Vlad.