I'll give you an out here. Kicks myself twice for this..
There is Decoherence from the moment Satan sinned until now. But that had no effect upon God, His Kingdom, His Purpose and Will. How Satan connects to Adam is where this discussion went [retarded]. Satan connects to Adam because 2 things here.
1. Satan = Enemy of God and His Creation
2. God booted Satan to Earth which is a place of His Creation to Adam
So yes, there is Decoherence with Satan this entire time. But with God and His Creation of Adam it is pure and harmonic.
Adam's decoherence begins when he sins, but Adam has no HISTORY of sin yet.
Satan is the History of sin, like I said 30 times now!!!!!!!
But Satan's history of sin [is not] Adam's History.
So for Satan, Decoherence began [AFTER] his original sin just like for Adam, his Decoherence began [AFTER] his sin.
No one had Decoherence prior to their sin.
Which also destroys the particle theory of sin!