Originally Posted by iaflyer

At the time that the DH reservation was booked/ticketing? All the time - almost every flight. The DH reservations are made as soon as you're name is on a rotation with a DH. You just add your name in TravelNet.

Of course the flight goes out with FC full, but that's because of upgrades at the gate. Look at the gate information screens, you'll see empty FC seats, that they then fill 30 minutes prior to departure.