I'm afraid I don't follow. Perhaps it will be easer to understand if you add a screenshot, or use specific examples? Thanks in advance for your clarification!

Didnt even knew this post was responded to, to make it easier basically because smart crates work with rules, you would create one smart crate with the rules that would apply to every song you would like to have in that crate. From that crate you then create a sub crate which applies all the rules from the parent crate but contains its own rules to have the specific songs you want in the sub crate. So if the parent crate has four different genres, the subcrates smart crates will the parent crate rules plus there own so you can have whatever you want as long as its in the parent crate. Hope that helped a little more.