If full expiation occurs before the general judgment, the soul is released from purgatory and goes to heaven. Fundamentalists note that biblical references to the judgment refer only to heaven and hell. It is at the general judgment that the justice and mercy of God will be demonstrated to all. Opponents of the Catholic position are generally silent about what happens to the souls of people who die long before the Last Day. There is no hint from Scripture that these souls remain in suspended animation.
Judgment is immediate which, by the way, is one reason why reincarnation is impossible.
It is here, between individual judgment and general judgment, that a soul may find itself in purgatory. That hardly accounts for the request of Monica, mother of Augustine, who asked her son, in the fourth century, to remember her soul in his Masses. This would have made no sense if she thought her soul would not be able to be helped by prayers, if she thought there was no possibility of being somewhere other than heaven or hell. Still less does the ascription of the doctrine to Gregory account for the graffiti in the catacombs, where the earliest Christians, during the persecutions of the first three centuries, recorded prayers for the dead. Such prayers would have been made only if Christians believed in purgatory, even if they did not use that name for it.