Good thing he's never claimed that. Rather it's Sean who gives Tissier that position, which might be fair if he stuck with the SSPX as the bishop did. But he didn't, because Tissier only gets ABL right when Sean says he does. Which, in for all intents and purposes, makes Sean the supreme authority on the Archbishop. 
Yeah I don't mean Ladislaus is the final authority, it just seems clear to me that Archbishop Lefebvre strained closer to flirting with Sedevacantism but just not quite holding it at some times, and was very inclined to want to make a deal with Rome at others. All that said I think even at his "Most Sedevacantist" he still *gave the benefit of the doubt* to the conciliar popes.  He just didn't have dogmatic certainty of faith that they were.
I don't know which side that's more convenient for, and I don't really care, I just honestly think its the truth.  Its possible thse pontificates are objectively dogmatic facts.  But if that's the case, than Lefebvre was wrong.