Return of an ancient enemy

I was going through my list of scribbled plot possibilities, and came across the following. It might be adaptable for Ourobos if he does want Dav'nalleous to make a reappearance from Extremely old character.

The Persona supernatural talent was introduced into House Tytalus by a sleeper Diedne fleeing the destruction of the Schism War. Was pretending to be a young Tytalus from a destroyed covenant.
In truth, he was supposed to introduce assorted Summoners to a Dark Spirit, that had been bound to service by a lot of Wicker Man sacrifices. Once enough Titanoi had made innocent seeming contracts with this Dark Spirit, the sleeper agent would perform the correct ritual, and the Dark Spirit would resurrect the spirits/souls of the leading Diedne magi who had secretly ritually sacrificed themselves to the Dark Spirit, into the bodies of the Titanoi.This 5th legion would then bring destruction to the enemies of House Diedne.

Finding Titanoi and convincing them to contact the Dark Spirit took time. The cleaning up of the corruption of House Tytalus undid almost all this work. Sleeper agent had to pass mission onto his apprentice, and the next apprentice, and so on.

Finally enough (=souls to be reincarnated) living Titanoi have contracted with the Dark Spirit. The special ritual is to happen at the following astronomical conjunction, but requires using resources now belonging to player's covenant.

One problem is that canonically the Corruption of Tytalus happened before the Schism War, not afterwards (and the atmosphere of suspicion the Corruption engendered was one of the factors that led to the Schism War).

An alternative reason for it taking so long could just be that there weren't that many Tytanoi left after the Corruption? In the immediate aftermath, only Kalliste and her fillii were left, although that might have increased a bit by the time of the Schism War.

Thanks for pointing that out.
I simply transcribed my old notes and trusted my old self. Maybe I shouldn't, as I know longer know what he was thinking.
Perhaps the sentence about the corruption of House Tytalas represented some other plot element I was playing with. Or was an a grammatically poor explanation of the previous sentence "Finding Titanoi and convincing them to contact the Dark Spirit took time".