The whole world has been a simulation since before the time of the hierophants. The persons who exist in it have no idea they are in a simulation, they do not even have the theoretical knowledge to easily understand what being in a simulation means.
It is a simulation at the macroscopic level: objects, like in a video game, that have generic and specific behaviors programmed into them, not elementary particles obeying a few universal equations.
Scrivings are a minor cheat, a way to get a deeper control of objects while staying in the limits of the rules of the simulation. Maybe even they are an extension that the design of the simulation intended to be reached by a sufficiently advanced civilization. The lost minute and hierophantic commands, on the other hand, are a full blown security hole in the simulation.
