The value of the unused ticket minus the change fee is good for 1 year from the original date of issue of the ticket. Also, if the value of a nonrefundable ticket is used toward the purchase of a refundable ticket, that ticket becomes nonrefundable. These are the official rules, though YMMV (your mileage may vary, i.e., you never know whether you can talk a customer service rep or supervisor into bending the rules).