Well, you are incorrect. If that were true, then God is speaking with forked tongue. 1 John 1:9 reads, "If we confess our sins, he is faithful and just, and will forgive our sins and cleanse us from all unrighteousness."
This is a promise of God. Either this is true or God is a liar.
The only sin that cannot be forgiven is the sin of not asking for forgiveness. Anyone, no matter what the sin, can ask for forgiveness, and if they do 1 John 1:9 promises that they will be forgiven.
What you have done is precisely what you said. You are going "beyond what is written or come up with ad hoc explanations that seem to fit some of the criteria."
What is going on in this Passage. How is it to be interpreted. The question we have is how can it be that these scribes could not be forgiven when we know for a fact that God can forgive any sin (1 John 1:9)
From the Catechism of the Catholic Church, the Navarre Bible Commentary, and the Ignatius Catholic Study BIble answers this question:
From the Navarre Bible Commentary:
From the Ignatius Catholic Study Bible:
With genuine confession comes forgiveness (1 John 1:9), but these people never confess their sin and never ask God for forgiveness. When they reject God's forgiveness unto their death, there can be no second chance. Their decision to reject God becomes permanent; it cannot be forgiven at that point, that is, after death.