I would personally summarize the Catholic position as affirming both the negative formulation of the doctrine, that outside the Church is no salvation and everyone outside Her perishes eternally, and also the positive formulation of the doctrine, that all who find salvation do so in some way through the Church. These are two sides of the same coin and must be interpreted in light of each other.
If anyone is saved outside the visible bounds of the Catholic Church, it would therefore be through some sort of real corporate union with Her, even if this union is not fully known by the individual. Such union might exist in cases in which a person is ignorant of their obligation, or even opportunity, to join the Catholic Church yet seeks to love and serve God to the best of his or her knowledge. This idea might connect in some way to the idea of “baptism of desire.” The early Christians believed that catechumens who died before receiving baptism could well have been saved because of their desire for baptism. This sets a precedent for the idea of God granting remission of both Original and personal sins and therefore reconciling a person with Himself outside the setting of the seven sacraments, or at least outside of the ordinary way in which they are administered.
This idea, supplemented by a conviction that God would not allow someone to suffer the torments of hell through no fault of their own, has led many to believe salvation may in some mysterious way may be granted to people who do not seem to have ever desired baptism explicitly, but who loved and served God to the best of their knowledge and who would have desired baptism had they been aware of what it is. It’s important to recognize though that if baptism of desire stretches this far nevertheless those who receive it become true members of the Catholic Church at least in the sacramental sense; they are not being saved outside it.
We should note before leaving this subject that, if I’m not mistaken, Church documents generally seem to use cautious language to describe this possibility. If this sort of baptism by implicit rather than explicit desire happens at all, it happens in a sort of hidden way. We therefore can’t say with certainty that it ever has or ever will occur; we can only express what we suspect happens.
Finally, we must note the situation of the apostates, heretics, and schismatics. These people are baptized and therefore in a sacramental sense members of the Church, yet if morally responsible for their apostasy, heresy, or schism have separated themselves from the fullness of Catholic unity (and therefore from God who meets man in the Catholic Church) and so also cannot be saved. Nevertheless, we can recognize the possibility of someone objectively holding opinions incompatible with Church doctrine or being a member of a schismatic Church or ecclesial community, yet honestly, through no moral fault of their own, believing themselves to be faithful to the fullness of the Christian faith and a member of the Church that Christ founded. If this is the case, it would not appear the person is subjectively responsible for or conscious of their external disunity with the Church of Christ, and so internally, morally and spiritually, they are faithful Catholics (under whatever other name), as well as sacramentally a member of the Catholic Church. Being materially but not formally separated from the communion of the Church is not a moral fault and so could not affect the salvation of someone who has been reconciled to God in baptism. Again, whether this situation ever occurs in real life is subject to dispute; we can only voice what we suspect to be the case.
Again, this is only my personal take on the matter as an individual lay Catholic.