If not for certain Nerfs, Both would have come out of TS Training with CoC Coating,
Cuz you're basically Applying your CoA Lessons on CoC,
Zoro Finished his Training & Fully Mastered CoA, but He didn't know He had CoC,
Luffy knew He has CoC, but his CoA Training was Incomplete as Rayleigh left 6 Months Early,
So when Luffy Finished his CoA Training in Wano, He was only a Thought away from Unlocking Adv. CoC,
While Zoro only needed to Discover that He has CoC,
This is why both Unlocked it the Moment They thought about it,
It's just Result of Training with Legends, a Privilege that Most People don't get, including Most CoC Users,
They were simply Delayed for Story Convenience.