I recently tried to book a trip for July (CVG-RNO) using my Amex Delta $99 companion certificate. When I checked availability for L,U,T seats using the normal booking process I found seats, however, when I started the process by selecting the e-certificate, voila, I got the message that there were no seats for the location/dates I selected. I even plugged in a Wednesday-Wednesday timeframe and got the same results.

Are these $99 companion certificates worthless with Delta's capacity controls? If this is the case, I'll have to seriously considering cancelling my AMEX card. Is there a good time to look for these seats, or should I just keep checking often?