How does the adherence to Go's spec of a compiler affects its legality with regards to the compiler's name? And why is that an exception if it is a backwards co

How does the adherence to Go's spec of a compiler affects its legality with regards to the compiler's name? And why is that an exception if it is a backwards compatible superset when a new version of the "real" Go could come out with new features that are incompatible with the extensions (thus rendering the previously compatible superset now incompatible and presumable illegal)?