I'm not one who holds the Thuc line to be doubtful, but Bishop Webster's line has some issues due to one Jean Laborie.
Bishop Webster was consecrated a bishop by Bishop Slupski (I don't believe there are any doubts about his line).
But he had been ordained to the priesthood by Bishop Timothy Henneberry.
Henneberry, in turn, was consecrated a bishop by a Bishop Terrasson.
Terrasson had been consecrated by Clemente Dominguez Gomez (of Palmar fame). Apart from the fact that Gomez had no training and could easily have botched the Rite of Episcopal Consecration, this was likely valid ...
except, and here's the problem
Terrasson had been ordained a priest by in 1974 by Jean Laborie.
But in 1977 Bishop Thuc CONDITIONALLY consecrated Laborie. There's no record of who ordained Laborie, but his pre-1977 consecrationS (plural) went as follows ...
[Laborie] had already been consecrated a bishop on 10/02/1966 at xxxxx by Jean Pierre Danyel, a bishop of the Sainte Église Celtique. Later he was consecrated sub conditione a bishop on 08/20/1968 at xxxxx by Louis Jean Stanislaus Canivet, a bishop known as "Patriarch Aloysius Basilius III" of the Patriarchate Orthodoxe de l'Europe Latine.
So his status in 1974 when he ordained Terrasson to the priesthood was one of clear positive doubt. So much so, that in 1977, Bishop Thuc consecrated Laborie conditionally.
NOW ... there's an allegation that Terrasson had been conditionally ordained at some point before his consecration by Clemente. But I've seen no proof for this whatsover.
So unless there's docuмentation/proof that Terrasson had been conditionally ordained before his consecration, the whole line is in doubt.
Consequently, we have to hold there to be positive doubt regarding the validity of Bishop Pfeiffer.