I want to throw this out but if Sanji does get CoC, I don't think he'll be able to use AdCoC like Luffy, Kaido and BM.
Kaido said only a few can do it which makes me think only those who are specialize in CoC are the only ones that can do it.
The ones who have CoC but specialize in another haki uses CoC to level up their specialty.
Kat has CoC but his specialty is CoO, don't see him getting AdCoC, he had 40+ years to learn it from BM.
Doffy has CoC but I'm pretty sure his specialty is CoA given no one can break his Birdcage.
Zoro attack wasn't AdCoC but it seems there was a base of CoC to it that it let him scar Kaido. Even with that, Luffy's AdCoC base punch > Zoro's Asura.
If Sanji does unlock CoC, I think it'll be used as a base for his CoO to be higher.