One small correction:  Each profile covers all ratified extensions (relevant to that profile, e.g. all Supervisor-level extensions for an 'S' profile), and categories each extension in one of four categories (Mandatory, Supported Optional, Unsupported Optional, Incompatible).

So in one sense a profile is a set of ALL relevant ratified extensions.  But from a perspective of which extensions are Mandated by a profile, that of course is a subset of all relevant ratified extensions.  When people have talked about treating profiles like extensions in tech-config insofar as discovery of whether a profile is implemented or not, that has been wrt to the Mandatory subset of the profile.  Any Supported Optional extensions within a profile that are actually implemented by a design would still have to be separately discovered as being implemented.

Greg