I’m not convinced that the third example is in fact an instance of the “discount” sense of the word. We’re told that “this” does not defray the cost of paying interest, but we have no idea what “this” refers to. I see no reason to assume that’s its a discount.
In fact, I think it isn’t. I think the passage refers to something like a government railway, and the sense is something like:
“[Revenue from fares] does not quite defray the interest on the cost of [building and equipping the railway], inasmuch as it barely comes to 31% [of that cost], but [this is because] rates and fares are deliberately kept low to encourage [use of the railway so as to promote] settlement and communication.”
So, no discount. Fare revenue is not sufficient to defray - i.e. pay - the railway company’s interest bill. It’s the payment of bills sense.