To be absolutely and abundantly sure, the infallibility of the ordinary magisterium (what all the bishops teach in union with the pope) is
not Novus Ordo doctrine. It goes back at least to the Vincentian canon and St. Augustine (though admittedly not yet as precisely developed as it was afterward). It's in Saint Robert Bellarmine, the Doctor of the Papacy and ecclesiologist
extraordinaire:
.
The Church absolutely cannot err, neither in matters absolutely necessary, nor in others which must be believed or proposed that we must do, whether they are expressly held in scriptures or not... [by this we mean] that which all the bishops teach as pertaining to the faith necessarily is true and de fide... if all bishops would err, the whole Church would also err, because the people are held to follow their own pastors, by what Our Lord says in Luke 'He who hears you hears Me' and 'whatsoever they say, do (p. 124, trans. Grant).
.
Many solemn texts justify their definitions
based on what was universally taught-- Vatican I does this when defining papal infallibility (i.e., as a proof of it they point to the universal activity of the world's bishops), Pope Pius XII does this with the definition of the Assumption, and so on.
.
Is it any wonder, given the universality of this teaching, that among Martin Luther's condemned errors is this:
.
[Condemned proposition of Martin Luther, no. 28] If the pope with a great part of the Church thought so and so, he would not err; still it is not a sin or heresy to think the contrary, especially in a matter not necessary for salvation, until one alternative is condemned and another approved by a general Council. (Denz. 768 )
.
Bellarmine, as do later authors, expound on the infallibility of the ordinary magisterium which is indeed dependent on the pope. There is only
one infallibility at day's end, and it is the pope's, diffusing throughout the Church. As Parente puts it:
.
As man’s life is one but derives from the soul and is diffused through all the body, so infallibility is diffused and circulates in the whole Church, both in the teaching Church and in the learning Church, but dependently on the head (pp. 142-43, trans. Doronzo).