No one "opposing me" in this thread has had an ounce of theological training, so I shouldn't hold it against them, but in Catholic philosophy (St. Thomas Aquinas) there is the concept of "quoad nos" which means "from our perspective". You can describe things from God's perspective, or from our perspective ("quoad nos")
There is no "retroactive" anything. That makes it sound like winding back time, or giving a second chance. No, there is only the judgment of God, which happens at the instant of death as the Church teaches. But God can take all manner of things into account -- including future effects of that person's sins, future prayers offered on behalf of that soul, present prayers being offered, etc. before that Final Judgment With No Appeal is given...
"Who has known the mind of the Lord, or who has been his counsellor?"
Oh, and it's not about God choosing to judge someone innocent who was in Mortal Sin. In the cases we're speaking about, God could grant the grace of CONVERSION, or PERFECT CONTRITION, to a sinner before he dies. That soul would still have to undergo pains in purgatory.