Can humidity get inside the cigars in a sealed box?

That is correct, opened boxes and unsealed boxes benefit from the humidity controlled climate, but boxes sealed in plastic do not allow humidity to get in or out. This type of packaging was designed to allow the cigars to retain a maximum of moisture from the time they leave the factory to the time the box is opened by the consumer. It is important to keep them in a cool climate (we keep ours between 68-70 degrees) to avoid beetles. The other way we make sure that our cigars are fresh is through rigorous inventory management.