Two counterpoints here. First, the “N-tet” is in many cases more a matter of counting than of artistic intent. The difference between the Joe Bloggs Quartet and the Joe Bloggs Quintet is often no more than the fact that one more musician got hired for a particular session.
Second, and somewhat related, is that how a record got billed has (at least historically) had more to do with the record company than the artist themselves. Take the Monk example I gave above - I guarantee you it was not Monk’s decision to release one album as a quartet and the other under only his name.