Basically, Chinon and Ricoh were using the K-mount with some sort of licensing agreements. Ricoh actually had a slight variation but those lenses would work on Pentax cameras. Sears had some decent lens in what was called a pkr mount. Sometimes those lenses can cause problems on the new digital Pentax bodies but sometimes not. I have 3 of those lenses. I have 2 copies of the model 202 135mm f2.8 lens, one got stuck when I tried to use it on my K200d and the other didn't. I strictly use them on the film bodies because of that.
Some people have removed the Ricoh pin but I didn't want to do that. I have the Sears 80-20mm and the Ricoh pin causes problems on the k200d as well.
Anyway, when Chinon went autofocus, the lens compatablilty shifted. Those Chinon AF lenses won't work on Pentax bodies. Vivitar also had some cameras made with k-mount bodies and Sigma did as well. Sigma also has a mount of their own. Ricoh and Chinon are usually the best bet for film bodies as long as you stick with the manual focus bodies. I think you can use mf pentax lenses on the AF Chinon bodies but am not sure.