Contrary to popular belief, most SVs are not dogmatic SVs and they know that consensus would be impossible due to the large portion of the Catholic world that still considers these popes to be legitimate. And, in fact, most of the dogmatic SVs happen to be sedeprivationists, and in their view the formal vacancy CANNOT be filled so long as the Holy See is being materially occupied.
Lad, you say most SVs are not dogmatic, yet they label themselves; "Sedevacantists" - which specifically means to broadcast the fact that, FRANCIS IS NOT THE POPE. While I agree that, that in and of itself cannot be 'defined' as dogmatic, if it were possible tho, it would be dogmatic far as they are concerned whether or not they admit to it - no? Perhaps some SVs can chime in here.
Consider Sedevacantist Mithrandylan who posted as Nado for +1000 posts before being banned. We saw him get an awful lot of likers and an awful lot of upthumbs from presumably his fellow SVs. What I am getting at is that SVs believe different from non-SV trads, hence their practice or Lex Credendi is different as well - I think this is because they have a different Lex Orandi. I think their Lex Orandi goes out of it's way to, not only specifically exclude the conciliar popes, but to also condemn the conciliar popes.
"This famous Una cuм of the sedevacantists...ridiculous! ridiculous .... it’s ridiculous, it's ridiculous. In fact it is not at all the meaning of the prayer "- Archbishop Marcel Lefebvre, retreat at St-Michel en Brenne, April 1st, 1989
Source
Moderate SVs would agree with this. And even some dogmatic SVs like the Dimonds agree with this. So it's a side issue.
Again, SVs, whether deemed to be moderate or not, all do something they are not permitted to do - omit the name of the pope from the Canon. Because it has to do with a giant thing in the Mass, i.e. the Canon, this is a giant thing in the Law Of Praying, i.e. the Lex Orandi.
I mean, what about Pope Benedict XIV in his encyclical
Ex Quo wherein he repeats numerous times that it doesn't matter what anyone thinks, it is a sin to omit the name of the pope from the canon of the Mass. That's it and that's all of it - period.
"Roma locuta; causa finita est". Mind you he is specifically speaking to the Eastern Church - yet the one thing the Eastern Church has in common with SVs of today, is that they both insist that the pope is not the pope, yet Pope Benedict XIV pretty much repeated the same thing over and over stating: whoever omits the name of the pope from the Mass *for any reason* separates himself from the entire world.
"It is generally agreed that those who do not for any reason recall the memory of the Apostolic pontiff in the course of the sacred mysteries according to custom are, as the blessed Pelagius teaches, separated from the communion of the entire world"
I understand SVs will argue the pope is not the pope, I get that - I may be dense, but not that dense. But SVs somehow think their argument is different - but when it comes right down to it, it's not, it is the same argument. Both have the same opinion that the pope is not the pope.
As I hope you know, I have a lot of respect for both your and Matthew's views, and I readily admit that I am way, way less educated in these matters. Yet I think the Lex Orandi is dictating the very real and serious differences between SVs and non SV trads. I will however gladly accept correction where correction is due.