This evil and dangerous doctrine of "the final salvation of all mankind,".... and that progression has been a main focus of this thread. I would trace its development as a perversion of God's desire to save "all men" into the idea that God gives all men sufficient grace for salvation. A more traditional understanding of this phrase in various senses is expressed by St. Thomas in the Summa, First Part, Question 19, Article 6, Objection 1:
1. God does give all men sufficient grace for salvation; this is infallible from Scripture.
a. St Paul tells us that "God wills that all men be saved and come to the knowledge of the truth." (1 Tim 2)
b. St Paul tells us that "God will not permit you to be tempted beyond your strength."
c. Conclusion - All men, if they respond to grace, can avoid sin, which will merit them sufficient graces to know the Truth (i.e. Church), then persevere to salvation.
d. This is infallible.
2. Salvation is a mystery. As Fr Wathen pointed out, no one can fully understand how God works/deals with others in their life, since we don't even understand the ways in which God works in our own life.
3. Since salvation is a mystery, so is the idea of predestination. I don't pretend to understand St Thomas' ideas as they are beyond me.
Salvation in Christ Is Offered to All
10. The universality of salvation means that it is granted not only to those who explicitly believe in Christ and have entered the Church. Since salvation is offered to all, it must be made concretely available to all. But it is clear that today, as in the past, many people do not have an opportunity to come to know or accept the gospel revelation or to enter the Church.
The errors of V2/JP2 on salvation is not, in my opinion, that "salvation is offered by God to all". The error lies in the prideful idea that it is "concretely available", or that God's ways can be understood by man, or that God's work in our soul, through our conscience, His Divine Providence, and such "spiritual coincidences" can be known, materially (i.e. that grace can be measured).
Thus, this leads to the V2 heresy that those "who do not have the opportunity to come to know or accept the gospel or enter the Church" weren't "given a chance" by God. Horrible blasphemy this is! Because, as St Thomas (and many others tell us), God does not cast pearls before swine, and many do not get graces because of sins. If you can't/don't want to follow the natural law, then you've already damned yourself. You don't need to hear about the gospel or the Church, if you're on your 4th marriage or your a drug dealer for life.