I don’t know if you have ever come across the term ‘Theological Notes’. This is what both you and Bishop Lefebvre seem to be speaking of. This is not in dispute. Both sides acknowledge this fact. The Council itself made this clear when it differentiated their Dogmatic Constitutions from their Decrees. All of them, however, were officially promulgated as documents of an Ecumenical Council and as such have the full authority of the Church’s extraordinary magisterium. These pastoral regulations have always been held as binding in the Church.
In past councils these regulations were included in individual canons alongside declarations of dogma. Yes, they could be overturned (and, in fact, have been overturned in the past), but only by a separate exercise of extraordinary magisterial authority, such as another ecumenical council or papal exercise of extraordinary magisterial authority as head of the universal college of bishops (not
ex cathedra as that instance of extraordinary authority only pertains to matters of faith and morals, not procedural regulations).
When I speak of denying the authority of the Council, I don’t mean analyzing the theological notes, I am speaking of rejecting the binding authority of those aspects of the decrees which have no theological note. The
SSPX website describes in length the concept of theological notes, but seems to classify
everything with regard to theological note. It does not approach the fact that there is a good amount of the actual living out of our faith which has no context within the context of theological notes.
It is these aspects without theological note, those which lie outside of that 95% you cited, which the SSPX do not see as binding. If they were promulgated by the ordinary magisterium though general papal teaching or curial decree, then yes, they weren’t necessarily 100% binding and up to debate. They weren’t, however. They were promulgated using
extraordinary authority. As such, everything is binding. To challenge that 5% is to challenge the very nature of extraordinary magisterial authority.