I am confused, It doesn't make any sense.
In the episode "Bride and Gloom" when Zile and Dantalian tricks Prue into marriage and Piper and Phoebe were turned evil and they became Warlocks and the Book of Shadows also turned evil to due the connection to The Charmed Ones.
and when Phoebe and Piper got Prue divorced they turned good again, It makes sense but when Phoebe got married with Cole in a Dark Wedding which is basically the same thing, It didn't make any impacts on Piper and Paige or The Book, not even due to Phoebe's demonic pregnancy. She touched The Grimoire and she had demonic powers.
Come on! how much does it really take, He was The Source of all evil while Zile was just a warlock. Shouldn't Piper be turned again into a Warlock long time ago and Paige into a Half-Darklighter and Half-Warlock long time ago.