Wikipedia says that formal schismatics are those who:
knowing the true nature of the Church, have personally and deliberately committed the sin of schism.
But if formal schismatics have to truly know the true nature of the Church, is it ever actually a category that can apply to people?
For example, Protestants reject the authority of the Catholic Church and the Pope, and so would not be said, I would think, to know the true nature of the Church.
Likewise, are the SSPX truly formal schismatics if, in their rejection of Vatican II, they believe the true nature of the church is other than that of the Catholic Church after Vatican II?
If you have to know and truly believe in the true nature of the Church in order for your rejection of it to be "formal", then it seems to be that this is a largely academic category, and that there would be exceedingly few actual cases of formal schismatics.