Zoro not knowing He has CoC doesn't mean He was always using it since King Fight,
From his Perspective, his Swords are like Containers, He charges them with Haki, that's what King of Hell is,
After that, it's up to him to choose how to Perform his Attack:
1. Perform an Attack without relying on Haki that is Stored/Reserved inside his Swords ---> Such as the Usual "Rengoku Oni Giri"
2. Perform an Attack Powered-Up by Haki that is Stored inside his Swords ---> Becomes "King of Hell Rengoku Oni Giri"
3. Perform an Attack Powered-Up by Stored Haki + Keep his Haki Flowing into it ---> Becomes "Serpent-Sword King of Hell Rengoku Oni Giri"
They are basically like Two People fighting together,
Either He Performs an Attack like He usually does or He throws at you the entire Haki that his Swords can Store at a Time or He goes Max Output,
Adv. CoC is only Used when the Attack is Max Output (Meaning Serpent-Sword Style),
Which was only performed so far to Finish Off King,
From his Perspective, his Swords are like Containers, He charges them with Haki, that's what King of Hell is,
After that, it's up to him to choose how to Perform his Attack:
1. Perform an Attack without relying on Haki that is Stored/Reserved inside his Swords ---> Such as the Usual "Rengoku Oni Giri"
2. Perform an Attack Powered-Up by Haki that is Stored inside his Swords ---> Becomes "King of Hell Rengoku Oni Giri"
3. Perform an Attack Powered-Up by Stored Haki + Keep his Haki Flowing into it ---> Becomes "Serpent-Sword King of Hell Rengoku Oni Giri"
They are basically like Two People fighting together,
Either He Performs an Attack like He usually does or He throws at you the entire Haki that his Swords can Store at a Time or He goes Max Output,
Adv. CoC is only Used when the Attack is Max Output (Meaning Serpent-Sword Style),
Which was only performed so far to Finish Off King,