Invincible ignorance is not a doctrine, it is simply inculpable ignorance.
Inculpable ignorance of the true religion excuses a person from the sin of infidelity or heresy. But such ignorance has never been the means of salvation, since the Original Sin suffices for damnation and is only remitted by Baptism. No one can enter Heaven in state of Original Sin and one of the graces of Baptism is the remission of Original Sin.
Infallible MagisteriumCouncil of Florence:
"
The effect of this sacrament (Baptism) is the remission of every sin, original and actual"
Council of Lyons:
"
The souls of those who die in mortal sin or with original sin only, however, immediately descend to Hell, yet to be punished with different punishments"
Council of Florence:
"
It is likewise defined that the souls of those who depart in actual mortal sin or in original sin only, descend immediately into Hell but to undergo punishments of different kinds".
Pope Innocent III:
"
The punishment of original sin is the loss of the vision of God; the punishment for actual sin is the torments of everlasting Hell".
From the fact that a person could potentially live a righteous life according to his conscience and not sin against the true Faith because of ignorance, many have drawn the false and heretical conclusion that such a soul is saved, or be granted sanctifying grace, thus making ignorance a means of salvation.
The dogma of "Outside of the Church there is no salvation," means that no one can go to Heaven unless he is in the state of sanctifying grace and furthermore, that in order to receive sanctifying grace, the soul must be prepared for it by divine Faith. Baptism is the entrance and gateway to this spiritual life in Christ. This preparation of the soul cannot be brought by inculpable ignorance. Every Catholic must know and believe the truths of Salvation as well as receive the Sacraments dispensed by the Church to receive the necessary graces.
According to the Angelic Doctor himself, God in His mercy will lead the worthy, righteous, well disposed souls, to the knowledge of the necessary truths of salvation, even send them an angel, if necessary, to instruct them, rather than let them perish without their fault. If they accept this grace, they will be saved as Catholics. Inculpable ignorance has never been a means of grace or salvation.