One of my writing philosophies is "Small details have the biggest impact." The smaller the detail, the more it affects everything. If by no reason other than it becomes easier to fit in larger details and become a core part of the lore of your world.
One Piece.
In the world of One Piece you can gain power by eating a Devil Fruit, A Big Detail. But you also get power by doing kung fu super good, or having a magic sword, or using cool technology. All big details that viewers can take in and be whatever about. Sure, you can fly by kick REALLY hard.
How does one know their Devil Fruit? Its name and powers? Well, it was generally established that when someone ate a Devil Fruit they instinctively knew. That's why all Df users used the NAME NAME format for their powers, and why nobody ever went with "The Fruit of Ultimate Damnation" as their Devil Fruit name. And We Know that teenagers get their hands on Devil Fruits.
So why did Monkey "Casually drops 'Dragon is my dad' in conversion" Luffy never told anyone he had the "Human Human Fruit Model Nika"? The Human-Human Fruit was the one Tony Tony Chopper ate to become the talking Racoon Dog we know him as. So didn't Luffy say, "Hey, that's my Devil Fruit too." The answer is that the instinctive knowledge seems to have been retconned. Or Luffy "Dragon is my dad" of the Monkey clan managed to care enough about keeping his fruit a secret to do so.
Also, we know the knowledge is instinctive because we were told directly with the Giraffe Giraffe literally being explained to us. Sure, he didn't have full control, but he had an instinctive knowledge of the basics of his fruit powers. Brook didn't know what his fruit was until he ate and knew it was the Revive Revive fruit.
Now everyone know their DF because they read it in a book. Just a random book, with all the Devil Fruits. Except the two that were given to the Giraffe guy and his friend. Everyone just remembers what their fruit looked like and looked it up. You know, in that book that must be super popular for this to be and contain knowledge that the World Government might want to control. Like the Dark Dark fruit that allows you just steal souls, or something, he takes other's DF powers so it kinda up there in the "This should classified" listings.
And yeah, I'm ranting about a super small detail in anime, but small details are a big deal to me, because of how much they can impact a story. And this has a big impact because Devil Fruits are such a big part of the world and knowing how users know their fruit is something that allows viewers to accept the concept and move on to the punchy bits.
Honestly, I feel like One Piece has shifted from its main plot. Remember when Black Beard was built up to be a big villain, maybe The Big Villain? Looking for the One Piece, just like Luffy, to become King of The Pirates. Now we have the Liberation Army and Luffy is the "The Great Liberator", which is just... big sigh whatever, I guess.