What I've wished for often while shopping the K900 market is a handy guide to the model years and differences. However, absent that, I've ransacked the net, got all the factory paper I can get my hands on, and, of course, learned a lot from the members here.
So I feel pretty well prepared to play K900 Trivia, if anybody ever releases that game.
And I thought I should organize what I've learned and make it available to the community. Attached is a comparison chart where I've done that. I've ignored stuff like horsepower and wheelbase, because that's so easily googled up, and instead tried to concentrate on what you need to know to make sense of the cars on the market. (I'm sure we've all noticed that used and even new car salesmen can be pretty clueless about what they're trying to sell you.) I tried to keep it high-level enough to be a quick read, but still pack enough detail to be really useful.
If you have suggestions or corrections, please post below and I'll revise and re-upload accordingly.
(Incidentally, I had intended to make this a PDF, but the forum software's limit on those is nuts--19K! That was a small file even in the Apple II days. So I had to play around to find something that would work and JPG did. I hope it will be legible for everybody.)