Well actually Pope Eugene IV proclaimed in the council of Florence that even if you shed your blood for Christ if you do not abide in the Catholic Church you cannot be saved.
Pope Eugene IV, Council of Florence, “Cantate Domino,” 1441, ex cathedra:
“The Holy Roman Church firmly believes, professes and preaches that all those who are outside the Catholic Church, not only pagans but also Jews or heretics and schismatics, cannot share in eternal life and will go into the everlasting fire which was prepared for the devil and his angels, unless they are joined to the Church before the end of their lives; that the unity of this ecclesiastical body is of such importance that only those who abide in it do the Church’s sacraments contribute to salvation and do fasts, almsgiving and other works of piety and practices of the Christian militia productive of eternal rewards; and that nobody can be saved, no matter how much he has given away in alms and even if he has shed blood in the name of Christ, unless he has persevered in the bosom and unity of the Catholic Church.”
Fairly close to what is in Denzinger 714.
That makes sense because pagans and Jews are not baptised. Formal heretics and schismatics are in serious sin, because they are not in a state of invincible ignorance which would excuse it, rather, they have chosen to leave the Church.
The history of those years is very complex:
1431 C. began Basel Switzerland
1438 C. moved Ferrara Italy, Pope Eugene IV excommunicated all who continued to assemble at Basel
1439 C. moved Florence Italy, agreement of union
1439 Russian Church separated from Constantinople
1440 Patriarch Metrophanes II succeded Patriarch Joseph II
1441 Cantate Domino of Pope Eugene IV
1443 C. moved Lateran
1443 Patriarch Gregory III succeded Patriarch Metrophanes II
1445 C. ends
1450 Patriarch Gregory III in exile
1453 Fall of Constantinople
1470 Patriarch Gregory III defected from Rome
1569 Union of Lubin (Poland-Lithuania) new Muscovy border
1588 Moscow Patriarchate established via Constantinople