Pretty much, but I was thinking that the contact states in it's terms that for every unit of [Resource Y] you fail to deliver on any given exchange, you'll pay [F] silver. You have the option of paying the silver and still fulfilling the terms of the contract, or refusing and having them bomb/invade you to raid you, like you said.
That way if you are 3 units short on one of the visits and have spare silver you aren't completely screwed and can still complete the contract successfully to the satisfaction of both parties.
That way if you are 3 units short on one of the visits and have spare silver you aren't completely screwed and can still complete the contract successfully to the satisfaction of both parties.