You can go back and check the Caesar fight yourself. There is multiple instances of Luffy attacking and grabbing Caesar without the use of Hardening. The only other explanation is using basic invisible Haki.
What Luffy didn't know how to do was flow his Haki outwards. Coating wasn't the problem. Even when he flashbacked to Rayleigh and the Boa sisters, it was all instances of them flowing the Haki out of their bodies.
I got a little mixed up. It's coating -> Flowing/Barrier -> Penetration/Internal Destruction
What Hyogoro, Zoro and the Scabbards know is Flowing/Barrier.
Zoro can't know penetration/internal Destruction, as he was surprised at "The Haki Luffy learned from Hyogoro", when Luffy first used it against Kaido. If he knew it, he wouldn't have been surprised by it.
Whatever the case may be, if we want to call flowing/barrier the advanced version, then what Luffy does with Internal Destruction is a step beyond that. I guess we'll call it MCoA, for Mastered CoA.
What Luffy didn't know how to do was flow his Haki outwards. Coating wasn't the problem. Even when he flashbacked to Rayleigh and the Boa sisters, it was all instances of them flowing the Haki out of their bodies.
I got a little mixed up. It's coating -> Flowing/Barrier -> Penetration/Internal Destruction
What Hyogoro, Zoro and the Scabbards know is Flowing/Barrier.
Zoro can't know penetration/internal Destruction, as he was surprised at "The Haki Luffy learned from Hyogoro", when Luffy first used it against Kaido. If he knew it, he wouldn't have been surprised by it.
Whatever the case may be, if we want to call flowing/barrier the advanced version, then what Luffy does with Internal Destruction is a step beyond that. I guess we'll call it MCoA, for Mastered CoA.