Thank you Dave for your sharing of all this info. I'm not fluent enough yet in all this electronic stuff to actually grasp what you are explaining. Beyond the central idea that there was a change made, and that the 90 VSS is specific to the 90's car.
I suppose that if a 90 vss went bad you would be at the mercy of the aftermarket. I recall trying to buy one as a spare from my local chevy dealer and they said it was nla.
Thanks again for your sharing the light!
Tom