I don't care what paperwork ARchbishop Lefebvre signed or didn't signed. At some point in all of our lives we have signed something and later realized it was a mistake. Some people are even forced to sign docuмents. Or signed paperwork without knowing the content. Or signatures are often forged.
Anyway, one thing about Saints is that many of them are not perfect and yet they do all they can to please God. They are examples for us to learn from.
ARchbishop Lefevre is a Saint.
(Also, there are many Saints who might not be officially declared saints but are Saints with God.