For most of my cheeses, I do use rennet as well as the clabber. Clabber is really just mesophilic culture.
However, for cottage cheese I do not use rennet. And I have a "fake" parmesan that I make by just allowing clabber cultured milk to set up for a couple of days, then cooking curd, salting and pressing it. I do have raw milk, though, that I do not pasturize prior to culturing it for this cheese and I'm sure that the natural organisms in it contribute to the flavor, texture, etc.
And yes, it looks as though your math is correct.