Dear Clemens Maria, remember Rev. Connell, a personal friend of Msgr. Fenton and editor of the American Ecclesiastical Review after him, clearly considered the legitimacy of Pope Paul VI to be a dogmatic fact in Dec. 1965. In 1965, we don't need to talk about Ordinaries or anything else (that only applies today, 50 years of an alleged sede vacante later), as Fr. Connell says "the whole Church, teaching and believing, declares and believes this fact and from this it follows that it is infallibly true" in the year 1965 that the Pope was the Pope.
Actually, now that you mention it, Fr. Cekada did express publicly some thoughts precisely about universal acceptance etc, but it was in a conversation on Ignis Ardens which is now down. I think there's an excerpt of it on the Bellarmine forums somewhere, I may post it here later if I find it. It contains some interesting thoughts from Father, he also seemed to qualify somewhat his earlier position expressed in a discussion with Mr. Lane on the same forum that all bishops with ordinary jurisdiction could cease to exist, among other things.
Anyway, for purposes of this thread, suffice to say with Fr. Hunter "it is enough to say that if the Bishops agree in recognizing a certain man as Pope, they are certainly right, for otherwise the body of the Bishops would be separated from their head, and the Divine constitution of the Church would be ruined." The reason for this is because, "The Church is infallible when She declares what person holds the office of Pope". This is a dogmatic fact, infallibly proved by the authority of the Church no less than the canonization of a Saint, or the declaration that some specific book contains errors opposed to the deposit of revelation, or the like. As Van Noort puts it, "the ordinary and universal magisterium is giving an utterly clear cut witness to the legitimacy of his succession".
The only way 60 odd year sedevacantism can be saved is by positing that bishops appointed by the non-Pope/false Pope/material Pope/antiPope can become Ordinaries by said appointment. I don't agree with that theory, as it dispenses with the need for the Papacy altogether and reduces the Pope to a delegate of the Church, an error condemned in Vatican I. But that is a matter for another thread. Catholics should simply ask themselves, is a prelate like, say, Cardinal Burke or a Bishop Athanasius Catholic? Yes, clearly they are, even if like most Catholics today, they may hold a few errors in good faith. If they are Catholic, they are the legitimate authorities of the Church, which means we cannot separate from communion with them. Would someone really argue they don't recognize Pope Francis? If they recognize him and remain in communion with him, so must we, for we must remain in communion with them. The doctrine of universal acceptance is, therefore, simple Catholic common sense, which says we must remain in communion with the Sovereign Pontiff and the college of Bishops appointed by him if we wish to remain Roman Catholic. We can separate from individual Bishops whom we consider clearly heretical, on condition that they are declared as such later by the Pope, but not from the entire Apostolic hierarchy, nor from the Roman Church.