I've never been to seminary (like Matthew has), so I have not studied the topic, but I have heard various arguments for and against.
One of the explanations I have heard that defends Novus Ordo ordinations says that to be thorough with conditional re-ordination, one would have to endeavor to examine ALL of the sacraments that the Novus Ordo priest administered after his first ordination and before his conditional re-ordination. (Baptism is excluded because anyone can baptize, even a non-Catholic.) This means that everyone who had received Holy Communion from him should be notified that perhaps they received an invalid sacrament. If that sounds like a lot of work, how about confessions? Imagine trying to contact everyone who had gone to confession to that priest when he may not have been a priest at all. Their eternal salvation hangs in the balance. They would have to arrange for a general confession in which they try to recall all their past sins, especially those mortal sins for which they had been absolved by the priest in question.
Add to this the claim that never before in Church history has any priest's previous ordination been found lacking. Again, I have not studied this topic but I am only repeating the observations and arguments that I have heard.
I was just thinking about the possibility of a person innocent of all this goings on, and having 100% sureness that the priest they were going to confession was a priest, but in the eyes of God he was not for various impediments of today.
Not knowing the mind of God, but believing His Mercy don't you think that person's sins, even mortal were forgiven? Even if later, as the years went by and he discovered the possibility that some of the "priests" he depended on for sacraments were not priests at all once he was forgiven, his sins don't come back because he discovered about a particular priest.
Of course, if he wants to confess again, as we are allowed to do when in the confessional, mention a past sin previously confessed, he can but it would not be necessary as God in His mercy has already forgiven him.
That is my assumption, am I wrong to think this way?
Speaking from gut instincts and common sense, makes it hard to accept extreme consequences for what may appear to be foolish oversights or innocent mistakes in judgment.
We are not able to judge the internal forum. Only God knows the disposition of a person's heart. And in the end it is God's judgment that prevails.
But the Church has to go on objective reality when making rulings, and this comes into play when passing judgment on whether absolution is valid or not. Fortunately for us laymen we don't have to deal with these things.
Like I said, I have not studied Moral Theology or Sacramental Theology, but these are things a priest needs to learn, and certainly when he becomes a theologian he must study these topics
in great detail. Obviously, a non-Catholic so-called theologian is most likely ignorant of sacramental theology even if he has a certificate for "Theology."
There is such a thing as validity in giving absolutions, which is why all the furror over this recent "year of mercy" when Francis granted temporary jurisdiction for absolutions for the SSPX, and then the great news of him "extending indefinitely" the same power for these priests. If it was not important, it would not be a topic of discussion.
But IRONICALLY, Francis trivializes it by his cavalier treatment of the subject, as if he's just having fun throwing his power around like a simpleton playing with the levers of a great, modern bulldozer or a crane. We live in the age of unqualified leaders, apparently.
In the end, it is a good idea to review one's life and confess again sins that one believes have already been confessed and apparently absolved, in the past. I went to an SSPX retreat a few years ago, and that was the essence of the whole thing, to spend hours upon hours prayerfully contemplating all the sins of our past and reviewing them in confession to a priest whose time had been reserved for a general confession. (Protestants never bother to do anything close to that!!!) Those poor priests were really working overtime! Sometimes they were so tired that they even fell asleep while hearing confession. So does that effect the validity of their absolution??