It is a serious change. The Council of Florence and Unam Sanctum meet the 4 tests of infallibility and they exclude every non-Roman Catholic from eternal life with no room for exceptions.
ewtn.com/library/ISSUES/ORDIN.TXT
There are, clearly, four tests of infallibility: The Pope must be (1) intending to teach (2) by virtue of his supreme apostolic authority (3) a matter of Faith or morals (4) to be held by the universal Church.
" We declare,say, define, and pronounce that it is
absolutely necessary for the salvation of every human creature to be subject to the Roman Pontiff."
(Pope Boniface VIII, the Papal Bull " Unam Sanctum", 1302 A.D.)
" The most Holy Roman Church firmly believes, professes and preaches that
none of those existing outside the Catholic Church, not only pagans, but also Jews and heretics and schismatic’s, can have a share in life eternal; but that they will go into the eternal fire which was prepared for the devil and his angels, unless before death they are joined with Her. and that so important is the unity of this ecclesiastical body that only those remaining within this unity can profit by the sacraments of the Church unto salvation, and they alone can receive an eternal recompense for their fasts, their almsgiving, their other works of Christian piety and the duties of a Christian solder. No one, let his almsgiving be as great as it may, no one, not even if he pour out his blood for the Name of Christ, can be saved, unless he remain within the bosom and the unity of the Catholic Church."
( Pope Eugene IV, the Papal Bull " Cantate Domino", 1441 A.D.)
This change opens up more questions for me. If all popes are not in agreement how could they all be infallible? If the Catholic Church has the fullness of truth why didn’t they know about salvation for the invincibly ignorant before Vatican II?