Throughout the Christian ages, the Athanasian Creed was always and everywhere understood to mean no one was saved without the Catholic Faith, "Whoever wishes to be saved, before all things he must hold the Catholic Faith. Now the Catholic Faith is this, that we worship God in Trinity, and Trinity in unity ... whoever wishes to be saved must think thus on the Trinity. Furthermore it is necessary for everlasting salvation that he also believe faithfully the Incarnation of Our Lord Jesus Christ. This is the Catholic Faith, which except a man believe firmly and faithfully, he cannot be saved." This is Tradition, this is what we must believe and must defend, the necessity of the Catholic Faith.
The idea that this refers to a necessity of precept only is a novelty, first seriously suggested in the 15th and 16th centuries. But what is far worse than what was suggested, by Suarez and some of the Salmanticenses, which was generally regarded as a discredited minority viewpoint, is the utterly novel and heterodox idea that Jєωs, Muslims and pagans living in the midst of us Catholics, not on some distant isle, can be saved without the Catholic Faith and without knowing and loving Jesus Christ, dates practically to the 19th and 20th century.
OK, so until the 15th and 16th centuries it was believed "always and everywhere" that one cannot be saved without explicit believe without explicit belief in the Holy Trinity and the Incarnation. That would seem MORE than sufficient to establish this as infallible dogmatic teaching of the Ordinary Universal Magisterium. In fact, if that doesn't constitute such a teaching, then I have absolutely no idea what belongs to the Ordinary Universal Magisterium.
So now a "novel" opinion comes along, and a bunch of liberal / modernist types embrace it. So instead of this being "heresy", which it is to deny such a teaching of the Ordinary Universal Magisterium, the modern BoDer Pelagians call it an "acceptable minority opinion".