In the old days of paper tickets (and open segments - where the ticketing was separate from the reservation(s)) I did this a couple of times - once throwing away the coupons myself, and the other where an agent threw away unused coupons. Either the agent(s) are laid back and don't care or they don't know/understand the rules. The rules on the pper tickets clearly stated that the coupons had to be used in the order in which they appeared.