In the case of the Palmarian sect he may have admitted to withholding his intention but not for any other. He had plenty of opportunity to set the record straight. I question the accuracy of the Angelus article where they reported this. Supposedly he wrote a letter but I've never seen a copy of the letter where he admits to simulating any consecration. That article was written in 1982. In 1985 Fr Sanborn visited Bishop Castro de Mayer.http://www.traditionalmass.org/articles/article.php?id=60&catna
So if they already doubted +Thuc in 1982 why was Bishop Mayer sure that +Thuc's consecration of Bishop des Lauriers was valid in 1985?
Yet not even des Lauriers can read the internal forum to know whether intention was withheld (in a bishop who admitted to withholding intention during other episcopal consecrations).
Note also that, in this regard, the Church's rule (i.e., that intention is presumed to exist unless there is something in the external forum which evinces a contrary intention) would have failed.
In the case(s) where Thuc went through the form and matter, with nothing external contrary to the presumed intention, he nevertheless withheld it,
and the sacrament which by rule would be presumed to be valid was in fact invalid.
This goes back to the earlier question regarding whether, since there is question regarding the validity of the form in the Pfeiffer consecration, is there also question surrounding Webster's other sacraments/consecrations for the same reason (i.e., It was pointed out that when refugee conciliar priests come to the SSPX, and their ordaining bishop is investigated, if it is found he has a habit of violating the form of the sacrament, conditional ordination is -or was- usually given).
Same thing here with Thuc: He acknowledged withholding intention during his consecrations (which in addition to being evil, is invalidating and crazy).
If you are going to withhold intention, why go through the charade of pretending to consecrate???