So St. Thomas Aquinas may be in Hell right now in your world?
It is only possible, in so far as it was not God who revealed St. Thomas' sanctity, but an authoritative, albeit human, act of the Roman Pontiff. The fact is that the pope did not know the subjective conscience of St. Thomas.
Otherwise you have to say that it was revealed by the Holy Ghost. If it was revealed by the Holy Ghost privately to the pope, then it is not public revelation and is not to be believed as dogma or binding on the Church.
But the pope makes his canonization binding by virtue of his authority, so it cannot be said to be a private revelation, but PUBLIC DIVINE REVELATION, if it is infallible.
Or it is an act of the pope in his fallible capacity, and while binding on the Church, is NOT infallible, is NOT Divine revelation, nor is it part of the Deposit of Faith (like St. Peter's sanctity).