Expired dark chocolate or any expired chocolate is still very safe to eat and will not give you food poisoning or make you sick.
I've eaten expired chocolates including expired chocolate for years and never have I gotten sick from eating the expired chocolate.
Expired dark Chocolate is just not as fresh tasting so you may not enjoy it as much as you would if it were fresh and not expired.
But there's no problem with eating expired dark chocolates.
You can also use the expired dark chocolates for cooking with where you won't notice the stale taste.