I wanted to use my DL AMEX issued companion certificate yesterday, so I looked at available flights (ATL-DTW) and saw plenty of T fares on most flights on the day. So I clicked on 'View or Redeem Certificate' option and inexplicably, it only showed availability on two flights on the day of travel. So I went back to regular booking page and confirmed T fare availability. Lather, Rinse and repeat but no go.

Called the DM line, she transferred me to Promotions and the promotions agent couldn't book the ticket either - she also confirmed that the certificate should be usable on other flights, but it is not showing up in her system. Finally, she called someone and use an override feature to issue me tickets using the Companion Certificate.

Lesson: dl.com may not show all possible flights available for booking using companion certificates. I am not sure if this was a temporary glitch or a feature/bug.

I am glad that I was able to call and get this done - not sure if DM status helped or not. YMMV