Originally Posted by NHFL9
You can't get a voucher for the difference, you simply lose whatever you don't use. My recommendation is to buy a ticket of equal or greater value that is refundable. If you cancel the new reservation you will not get a new voucher. Hold the new reservation until you know where you want to apply the credit and then "change" that reservation.
The last time I spent a voucher, I got another voucher for the "change" This expired one year from that date. I had $1800 of them in 2003 I should know