CNAME records do not affect subdomains
For some reason, I believed that CNAME records affected subdomains.
For example, if I have this:
test.example.com. IN CNAME somethingelse.example.com.
I thought this would affect all record types (A, AAAA, MX, etc.) at test.example.com., which it does. I also thought it would affect names below it, such as www.test.example.com., but that is not true.
test.example.com. and www.test.example.com. are separate names in the DNS hierarchy, and a CNAME set for one does not affect the other.