Dear John:

For any teaching to be called "dogma", it must be a teaching that can be traced back to the early Church. "There is no salvation outside of the Church" is a dogma that has always been taught by the Church.

Understsanding of dogma, or any doctrine, however, improves with time and maturity. When a child asks where babies come from we tell them something truthful, but simple. As the child grows that simple understanding grows into a mature one. St. Paul teaches this principle in 1 Corinthians 13:9-13...

For our knowledge is imperfect and our prophecy is imperfect; but when the perfect comes, the imperfect will pass away. When I was a child, I spoke like a child, I thought like a child, I reasoned like a child; when I became a man, I gave up childish ways. For now we see in a mirror dimly, but then face to face. Now I know in part; then I shall understand fully, even as I have been fully understood. 

St. Paul does not say that we do not have knowledge. Rather, he says that our knowledge is incomplete and immature. Someday, like with a child asking where babies come from,  our knowledge will be complete and we will fully understand.

Our understanding of the faith, even of dogma, also matures. This is also true for the Church herself. This is called development of doctrine.

Father Hardon, in his Modern Catholic Dictionary defined development of doctrine as

Growth in the Church's understanding of the truths of divine revelation. Also called dogmatic progress or dogmatic development, it is the gradual unfolding of the meaning of what God has revealed. Always presumed is that the substantial truth of a revealed mystery remains unchanged. What changes is the subjective grasp of the revealed truth.

The source of this progressive understanding is the prayerful reflection of the faithful, notably of the Church's saints and mystics; the study and research by scholars and theologians; the practical experience of living the faith among the faithful; and the collective wisdom and teaching of the Church's hierarchy under the Bishop of Rome. 

 

Implicit in the development of doctrine is the will of God that the faithful not only assent to what he revealed but also grow in the depth, clarity, and certitude of their appropriation of divine faith.

To answer your first question, the Church did interpret this doctrine with a considerably more "hard line" in the Middle Ages. That is because the Church's understanding of this dogma was incomplete.

The teaching on salvation outside the Church, as Vatican II defines it and proposes exceptions, was not created by Vatican II. The Church has already been teaching that one does not have to be a card-carrying Catholic to achieve salvation. This was the basis of the conflict with Father Feeney back in the 1940s, long before Vatican II. 

Question Two: Our understanding of dogma is not dogma. It is the underlying and "substantial truth of a revealed mystery that remains unchanged", that is dogma. Our understanding today is not "wider," for Jesus said the road is narrow, but our understanding is more complete than in times past.

The child, in our example, changes his understanding of where babies come from as he grows up, but the essential truth of the information never changed, it was the child who changed. Before he looked through a "mirror dimly", later he knows the fullness of where babies come from.

Bishop Fabian W. Bruskewitz, perhaps the most orthodox and loyal bishop in the U.S., discusses this topic in his article, The Development of Doctrine.

God has given the task of understanding, interpreting, and teaching to the Church, not the individual, that is, to the Pope and Magisterium. As Jesus said in Matthew 23:2, we are to obey the man who sits in the "chair". When Ultra-Traditionalists challenge the man who sits in the Chair of Peter they violate and do violence to the very first traditaion — obedience — and this makes a mockery of the Bride of Christ. 

Jesus said that if we love him we will follow his teachings teachings (John 14:223-24). The opposite is therefore true too, that if we do not follow his teachings then we do not love him. Obedience to the Magisterium is one of the teachings of Jesus (Matt 23:2), thus those who disparage Vatican II and disobey current popes do not love Jesus, rather they love themselves, which is pride and arrogance, and make a magisterium to themselves thinking that they can officially define the faith.

Jesus said he would protect His Bride, and he has. There has never, at any time, been a pope who changed dogma or any infallible doctrine of the Church. It is not possible. Some have tried, like Pope Vigilius in the mid-6th century, but none of even come close to succeeding. Jesus does not lie, when he says he will protect his Church, he does it, he keeps his promises.

I hopes this helps.

God Bless,
Bro. Ignatius Mary