There is a certain point in any game where you have to decide how much research into how the world works do you want to do before playing. Some research is a good idea, but every person running a game can't research everything. That's how you get Batman in a city of under a million and so on.
Have you ever sat down and tried to figure out if there was enough farmland to feed everyone in your worlds?
Do all your dungeons have recreation rooms, storage, bathrooms, laundry, kitchens, etc...?
Your best bet, from my perspective, is look at the kind of details that are important to you and your players. Try and cover for and make sense of those sorts of things and take your best guess on the rest. An example would be I game with lots of computer geeks. If we play modern, future or sci-fi there is more to the digital side of things than there might otherwise be. The base knowledge of the players encourages/demands it. Our botany, on the other hand, is pretty limited so you could hand wave just about anything invovlving rare herbs and plants without anyong caring.