Chocolate is mostly fat, and fat picks up smells and dislikes temperature swings. A fridge offers both. Bars kept there bloom, go dull, and taste faintly of whatever else is on the shelf.
Keep a bar somewhere between 14 and 18 degrees, sealed, away from light. A cupboard on an inside wall is usually right. A wine fridge is ideal if you have one.
Treat a bar like a good olive oil, not like milk.
Unopened, our dark bars keep for eighteen months and the milk and white for twelve. The date is on the back. Once opened, wrap the remainder in its foil and finish it within a few weeks.
Ganache is different. It contains cream, so it does keep in the fridge, and should be eaten within three weeks of the date on the box.