Last November I got $600 in ticket stock printed transportation credit vouchers for taking a bump. They are issued as 4 @$150 each.
I've tried searching this forum and the FAQs but can't find answers to these questions -- so if any regular UA flyer can advise me I'd be grateful. Most of my flying is on NW.

First, is the only way to use these things to go to the airport or call for a reservation and then mail them in? NW vouchers are all electronic now so using them is very easy.

Second, with DL and NW paper vouchers, you used to be able to extend the expiration date by using them to purchase a refundable ticket before the deadline and then turning the refundable ticket back for another credit. Will this work with UA?

Thanks.

tom