Hussar
Legend
So what? None of the adventurers may have ever heard of the Caves of Chaos before the party stumbles onto them en route to somewhere else, but the Caves didn't just magically appear while the PCs were wandering by, and while the DM might have had them pre-placed the players would have made no decisions based on knowledge of the Caves, because they had none. Ditto the boxes.
This is a different point than the idea of history, however. Once something of any relevance appears in the gameworld its history must also be considered, as per the vampire example. I don't care why those boxes are sitting in the alley (or, conversely, why someone took them away and burned them last night), but I probably will wonder why nobody knew about something as significant as a vampire before now (knowing full-well there may be a perfectly good in-game answer).
Side note: I think a similar discussion has come up before, something to do with whether the guards at a town gate exist before the PCs interact with them in-game. And then, as now, I posited that they did exist.
A good GM needs to be an imaginer first, a communicator second, an engineer third, a facilitator fourth, and an author maybe last if only to afterwards record the story written in the game play, such as it may be.
Lan-"and a good measure of 'devious scoundrel' can also serve a DM well"-efan
That's not really true though.
If I'm playing the original Greyhawk boxed set, does that mean I can only use modules published before that boxed set was published? Once the campaign starts, can I use a module published after the beginning of the campaign? Because, if I do, then I've just made that dungeon "magically appear" while the PC's are wandering by.
Nothing in the game world exists outside of what the players have been directly told and experienced. Everything is subject to change at the DM's whim. If I decide that that tribe of orcs over there, that the players have never encountered or heard about, is now a tribe of gnolls, that is perfectly fine.
The only way it could be true that the guards at the town gate exist before the PC's interact with them is if the DM is forced to never change any setting details once the campaign begins. Does anyone play this way?