This doesn't seem right to me: RPGing happens in time, by people talking to one another. So it's a feature of the medium, not a regrettable limitation, that what is said is finite and focused.
So here's a point that, in my experience, comes up repeatedly in discussions about the nature and purpose of prep.
Some posters -
@Micah Sweet, perhaps you - treat the GM writing something up makes it, per se, a component of the fiction. Whereas to me, while writing something up is a fiction, it's not part of the shared fiction until it's shared. Its function, prior to being shared, is to serve as a type of constraint on, and prompt for, what the GM says.