Pope St Clement knew that non-Catholics could be saved from the beginning, for he wrote in about 95 A.D. to the Church in Corinth: “Those who repented for their sins, appeased God in praying and received salvation, even though they were aliens to God.” Catholic Apologetics Today, 1986, Fr William G Most, p 145]."
'Extra ecclesiam, nulla salus (literally, “outside the Church, there is no salvation”). Some people have wished to understand this saying in the most literal sense: that is, that the person who is not formally a practicing Catholic cannot be saved. The Church has condemned such an interpretation (cf. Denzinger-Schönmetzer, 3870-3873).
'This is not to say that the maxim is false. Properly understood, it is quite true. The Latin word extra can mean either “without” or “outside.” The correct interpretation and sense of the maxim is that we cannot be saved without the Church. It is through the Church, which carries on and makes present the salvific work of Jesus Christ in the world, that all who are saved reach heaven (even if it is perhaps only there that they realize it). Those who, through no fault of their own, have never known Christ or his Church can still be saved. But their salvation, too, is the effect of Jesus working through his Church. In a positive sense, this theological principle “means that all salvation comes from Christ the Head through the Church which is his Body” (CCC 846).'
Encyclopedia of Catholic Doctrine, OSV].