ultima,
You quote the Nota Praevia saying:
The rest of the things which the sacred Council sets forth, inasmuch as they are the teaching of the Church's supreme magisterium, ought to be accepted and embraced by each and every one of Christ's faithful according to the mind of the sacred Council.
Now, Paul VI's Credo of the People of God says this concerning infallibility:
We believe in the infallibility enjoyed by the successor of Peter when he teaches ex cathedra as pastor and teacher of all the faithful,[28] and which is assured also to the episcopal body when it exercises with him the supreme magisterium.
The "rest of the things" are of the "supreme magisterium", which Paul VI says is infallible.
The key here is in that the Nota Praevia says "the sacred Council defines as binding on the Church". This is referring to new definitions, of which there were very few. The rest of the Council's teaching was a reaffirmation of previous teaching or new disciplinary decisions.
What new dogmas were presented which were binding?
Lumen Gentium §21 contains a dogmatic definition of the sacramentality of the episcopate:
And the Sacred Council teaches that by episcopal consecration the fullness of the sacrament of Orders is conferred, that fullness of power, namely, which both in the Church's liturgical practice and in the language of the Fathers of the Church is called the high priesthood, the supreme power of the sacred ministry.
Fr. Congar comments: "It is difficult to see why the Council did not express a dogmatic decision on this point. But it would have been the only case of its kind." (qtd. in Catholic Counter-Reformation Jan. 1972)
Furthermore he says: "There are certain other questions upon which the Council does no more than to express, in a solemn manner, what is believed by all: one could even say that it is giving expression, through a unanimous act of the solemn magisterium, to what is the universal teaching of the ordinary magisterium" (ibid.). This is the case with religious liberty and collegiality.
The rest of the teaching of the Council was simply a reaffirmation of immemorial teaching from Nicaea I to Vatican I, which is reformulated and is still infallible, by virtue of the supreme magisterium. This is because the Conciliar documents were promulgated by Paul VI with the normal formulas for an infallible council:
PAUL, BISHOP SERVANT OF THE SERVANTS OF GOD TOGETHER WITH THE FATHERS OF THE SACRED COUNCIL FOR EVERLASTING MEMORY
The entire text and all the individual elements which have been set forth in this Declaration have pleased the Fathers. And by the Apostolic power conferred on us by Christ, we, together with the Venerable Fathers, in the Holy Spirit, approve, decree and enact them; and we order that what has been thus enacted in Council be promulgated, to the glory of God.
I, PAUL, Bishop of the Catholic Church
Compare this with the formula of promulgation used by Bl. Pius IX for Pastor Aeternus:
Pius, bishop, servant of the servants of God, with the approval of the Sacred Council, for an everlasting record.
Therefore, all the teaching by Vatican II concerning matters of faith and morals was 100% infallible, even if it is unfortunately phrased ambiguously at times (naturally the correct meaning is the one in conformity with Sacred Tradition and Holy Writ).
At last all which regards the holy ecumenical council has, with the help of God, been accomplished and all the constitutions, decrees, declarations and votes have been approved by the deliberation of the synod and promulgated by us. Therefore we decided to close for all intents and purposes, with our apostolic authority, this same ecumenical council called by our predecessor, Pope John XXIII, which opened October 11, 1962, and which was continued by us after his death.
We decided moreover that all that has been established synodally is to be religiously observed by all the faithful, for the glory of God and the dignity of the Church and for the tranquillity and peace of all men. We have approved and established these things, decreeing that the present letters are and remain stable and valid, and are to have legal effectiveness, so that they be disseminated and obtain full and complete effect, and so that they may be fully convalidated by those whom they concern or may concern now and in the future; and so that, as it be judged and described, all efforts contrary to these things by whomever or whatever authority, knowingly or in ignorance be invalid and worthless from now on. (Paul VI, Apostolic Brief "In Spiritu Sancto", read at the close of Vatican II by Msgr.Felici)
He wasted no time introducing into the Church a brand new Mass, for instance, which almost immediately ignored the liturgical guidelines set up by Council only a few years earlier.
The Pope is free to change disciplinary decisions of an Ecumenical Council, no matter how infallible it was.
What new dogmas were presented which were binding?
Lumen Gentium §21 contains a dogmatic definition of the sacramentality of the episcopate:
And the Sacred Council teaches that by episcopal consecration the fullness of the sacrament of Orders is conferred, that fullness of power, namely, which both in the Church's liturgical practice and in the language of the Fathers of the Church is called the high priesthood, the supreme power of the sacred ministry.