This actually answers the key question for me.
+Vigano says that it's morally certain that Jorge is not the pope.
+Vigano says he's not a "sedevacantist".
So how do they define the term "sedevacantist"?
When Bishop Williamson says that +Vigano stopped sort of sedevacantism (but doesn't rule out that +Vigano might go there), he subtly defines what he means (and likely +Vigano means, since they talk often).
+Williamson:
he may well himself share the conviction of many serious Catholics that this or that Conciliar Pope, anywhere from John XXIII to Francis inclusive, has not been a true Pope, but that conviction, shared by however many of them, can never amount to an official Church declaration
So, for them, the term "sedevacantist" refers to holding that all the V2 papal claimants were not legitimate.
We see also here Bishop Williamson's attitude about sedevacantism, calling it "the conviction of many serious Catholics". Hardly characterizing it as some "danger to souls" that must be avoided at all costs, as Plenus Venter alleged the Resistance holds. Of course, we also have a CI member who posted some correspondence with Father Chazal, where Father Chazal also holds that Bergoglio is not a true pope.
As for the "official declaration" part, I think almost every sedevacantist and certainly every sedeprivationist would absolutely agree with that, so that does not distinguish them from sedevacantists.
+Williamson also hints at the MAJOR of "sedevacantism", as I've laid it out before.
Has he not joined the ranks of the “sedevacantists,” ie. those Catholics who consider that the See of Peter has been vacant ever since that accursed Council did so much damage to the Catholic Church? How is it possible that truly Catholic Popes presided over that Council and its aftermath?
But, Your Excellency, Archbishop Lefebvre answered this question quite clearly:
ultimately I agree with you; it's not possible that the Pope, who is protected by the Holy Ghost, could do things like this. There we agree; it's not possible, it doesn't fit, this destruction of the Church ...
Archbishop Lefebvre only hesitated on account of the MINOR, and the certainty with which he could explain how this destruction could have happened.