Legitimate code holders are the ones that don't choose cheat powers. if you choose a cheat, you are disqualified from being a code holder. The last one that existed was apparently that priestess of the church who kept it a secret cause she knew being a code holder is so much more valuable than having a cheat power. so hinako is a rarity. She can activate and command ancient devices, possibly has administrative access to the powers of the world itself which designed such monsters as the giant god and the giant god killer and the mecha. a legitimate code is basically the keys to the world it seems like and you cant get it if you have a cheat power.The crux is that we still don't know what the cheats even ARE, how they can be taken and what was the purpose of setting the cheat system in such a manner that still allows choice.
It looks like some form of energy or power that is shaped into a cheat to standardize them and disable the crazier outcomes. But then Junko was able to get two without needing the supply extra energy herself, so that doesn't quite fit. Or maybe the energy needed to create a cheat is far smaller than what is removed.
Do legitimate code holders power the ancient devices? As a pure energy source alone, that's pretty incredible. It's unlikely to be mana since Hinako has had no effect on Elis' magic, but something else that shapes the world with Hinako's will rather than the spirit's.