I understand the term well enough to know the tropes when I read or hear them. If you’re not, you’re flirting with it and I suspect know more than a few.
You know far less than that for which you give yourself credit. (Heck, I’ve written for the Vatican paper L’Osservatore Romano. I can assure you that under its modern editors no sedevacantists or crypto sedevacantists get published there.)
I suspect you’re confusing sedevacantists with Lefevrists. I attend a diocesan ordinary form (Novus Ordo) mass daily and the diocesan extraordinary form (Traditional Latin) mass most Sundays. Sedes and SSPXers wouldn’t be caught dead at either ;-)