Most of the people who post here are young, so they did not experience what was happening in the traditional Catholic movement in the early years. I'm not young, lived through the changes, and have familiarity with what was going on, as I witnessed some of it firsthand and met some of the main actors. (I met Father Sanborn not too long after he was ordained in the mid 70s.)
The fact that something has the appearance of holiness, and amasses followers, does not make it holy, as I'm certain you realize. Nor does the mere appearance of holiness evidence validity.
Check out the link:The Apostles of Infinite Love – Magnificat
Then do a google search to find out the history involved.
It is true that a priest consecrated as a bishop by Archbishop Thuc would be validly consecrated, but that begs the question: Did he actually consecrate bishops? How would a person determine whether he actually did?
That's the very matter in contention.
On this particular "Thuc line," no one can demonstrate the issue with any certainty at all, as everything was purportedly done in secret and there were less than 6 people who made the initial allegation (they are all now deceased).
The SSPX never had anything to do with the so called "Thuc line" bishops, as the SSPX believed their validity to be doubtful at best, assuming they even actually took place.
Father Sanborn himself held that position for years.
Contrast that with the episcopal consecrations conducted by Archbishop Lefebvre: done out in the open air, filmed on television, with thousands of people present, another bishop involved, and dozens of other clergy in attendance.(2) Archbishop Lefebvre Consecration Sermon June 1988 - YouTube
I could never base my salvation simply on the word of two laymen who produced a couple of alleged photos and wrote on them.
What does that prove?
And although Father Sanborn is a valid priest (as I stated, I first met him in the 70's before the "Northeast Nine" episode), I would not consider him a bishop. Ditto for Father Dolan, now deceased. Same for Father Kelly and the dozens of other, what at one time were called "garage bishops" (as in, a bishop in every garage) due to the fact that so many of them were being "consecrated" in the so called Thuc line.
There are hundreds of bishops who were allegedly consecrated by Clemente Dominguez, who ostensibly ended up as the first pope without eyes. He has had several successors.
Archbishop Thuc was at one time involved with this group.Iglesia Catolica Palmariana (palmarianchurch.org)
Same for Mr. Schuckardt, whose group I came in contact with in the late 70s.
Frankly, I don't know why anyone would entrust their salvation to any of these fringe groups. It is unfortunate that "the Nine" could not remain in the SSPX. As time goes on, their claims to validity become more dubious, and their numbers dwindle to insignificance.