If you're not familiar with the concept of "canon" in fictional worlds, the idea is that some things are part of the world, some things aren't, some might be, and some are in an undetermined state. Usually, anything that the primary author(s) write is automatically canon, and things written by others isn't. There are also degrees of canonicity. For example, if something in a Star Wars novel contradicts something in one of the primary movies, the movie is the last word on what is "real" in the universe of Star Wars. (Actually, the last word is really George Lucas himself, as the world's primary creator.)
We do something similar here. The Foreworld Cabal is the originator of the canon and determines what is part of the Foreworld universe and what isn't. But there is lots of wiggle room for other people to make stuff up, because the world is really, really big. We love the idea that what other people make up will also become part of the world, so we're basically looking for opportunities to make that happen. But it has to be consistent of course, and we want to keep track of what's canon and what's not to the extent that we can. And so Mark is the guy who, because of that encyclopedic grey thing inside his head, gets that task.