What you say is not strictly true about koryu or waza. One could say that no two situations would ever be the same from a distance, position, timing etc. For this reason we have henka. We can do a particular waza with a specific variation. But that waza must still contain the fundamentals of a school. My school "always" does henka for public exibition/demonstrations. I do not allowed students to show the original as it still "mongai fushutsu". Not the be taught outside the gate. That's why we have the kata (the breakdown) To set in stone the fundamentals and possibly rearrage them. It's still X Ryu doing X Ryu. Not X Ryu making it up so that it's no longer X Ryu.