Interview with Fideliter magazine, 1990:

Fideliter:  Father de Blignieres, the Abbe de Nantes and Dom Gerard have virtually accused you of lying when you stated that you did not sign two Council docuмents, ‘Dignitatis Humanae’ on religious liberty and ‘Gaudium et Spes’. The magazine “Sedes Sapientiae” reproduced a docuмent drawn from the Vatican archives on which figured your name written in your hand. What is the truth of this, and what is this docuмent?

Archbishop Lefebvre:  The idea of interpreting signatures to signing an approval of Conciliar docuмents germinated in the more or less malicious brain of Father de Blignieres. The approving or refusing of docuмents was obviously carried out for each Council docuмent on its own. The vote was secret performed on individual cards, and done with a special pencil which made possible the electronic counting of the votes. The cards were picked by the secretaries from the hand of each Bishop voting, The large sheets were circulated from hand to hand among the Council Fathers, and where each one put his signature, had no meaning for or against any of the docuмents, but merely signified our presence at the voting session for the four docuмents. One would truly have to take the Council Fathers who voted against the text for weather-cocks turning with the wind, when one gives people to understand that with their signatures on the sheet they approved of what they had disapproved of half an hour beforehand in the vote itself.
One sees what can be expected from the imagination of people who truly are weather-cocks and who are now adoring what they burnt a little while beforehand, such as Father de Blignieres, Dom Gerard and the fightingest weather-cock of them all, the Abbe de Nantes.

Bishop Tissier de Mallerais' biography of Archbishop Lefebvre confirmed that the Archbishop signed all the Conciliar docuмents.

+Tissier's error in research was brought to attention after the printing of the biography.  He was unaware of, or had forgotten +Lefebvre's statements to Fideliter regarding this.

I doubt that +Tissier was "unaware of, or had forgotten" anything, as that was a very big controversy at the time.  Below (in the link) you'll find a thorough writeup of the entire thing.  +Lefebvre clearly gave his vote of non placet for Dignitatis Humanae but then in the end signed all the docuмents, deferring to whom he believed to be the "Holy Father".  There was room on the final signatures to indicate in the margins whether one was signing all four or just one or some of the docuмents on a page that combined 4 of them.  But, once again, who cares?  +Lefebvre was permitted to change his mind on the subject.  What is this attempted deification of Archbishop Lefebvre, to the point that some people would have their "faith" shaken if it were ever brought to light that he made some mistakes or errors in judgment?  I mean, he made a terrible error in judgement by selecting +Fellay for episcopal consecration.

https://www.catholicculture.org/culture/library/view.cfm?recnum=857

In 20/20 hindsight, after having had decades to analyze them, it is apparent that Catholic bishops should have signed none of the docuмents.  But it wasn't as obvious then.  Evidently, there was one bishop, Arrigo +Pintonello, who refused to sign any of them.  As a result, a fair bit of mythology has grown up around +Pintonello, that he consecrated this, that, or the other individual ... though without a shred of evidence to back it up.

There was no error in Tissier's research. +Lefebvre did indeed signed all the docuмents out of respect for the Holy Father at that time and in believing that the Council docuмents could be interpreted in the light of Tradition, something that was obviously becoming untenable due to the liberal interpretation that was accepted by the post-conciliar popes in practice vis a vis ecuмenism (Assisi) and religious liberty (removal of Catholicism as the state religion in many countries).

In essence I believe that "interpreting the Council in the light of Tradition" is similar to Benedict XVI's "hermeneutic of continuity" which sadly Ratzinger held firmly all the way to his grave.

Right, and to be all up an arms over the issue, getting all defensive about is, is to give the "argument" the same weight that Salza et al. are trying to attach to it.  +Lefebvre clearly did vote non placet on the docuмent but later deferred to the "Holy Father" (Montini) in ultimately signing.  So what?  He could have changed his mind before the ink was dry, or months or years later.  This is a confusing crisis, and I actually view it in a positive light when someone changes his mind every once in a while, a sign that the individual is intellectually honest rather than marching to some predetermined agenda.  Many of us were on boad with the Conciliar Church for years before becoming Traditional Catholics.  What does that matter?  Had he initially voted placet but then later changed his mind, it would still not be a "stain" on him.  It's easy to sit here as armchair quarterbacks 60 years later with the benefit of hindsight and decades of analysis.

It has been many years since I looked into this controversy, and so I do not recall all the details, but i believe the reconciliation between Msgr. Lefebvre's denial of ever having signed the two docuмents, and l' Abbe Brian hαɾɾιson's "proof" that he did, was that the docuмents offered as proof were actually mere attendance logs, and not actual vote logs for the docuмents themselves. 

The proof of this was the existence of signatures of other proxies appearing on the same list bearing Msgr. Lefebvre's signature (i.e., but while proxies were permitted to attend the sessions, they were not permitted to vote).  Consequently, a list containing the signatures of proxies could not be an actual voter record.