AANYC1981

DCA-LGA and was happily in C+ and the agent came on board to UPG me to FC....no PDB for me since it was last minute but would have been nice since we had to sit for 30 mins in the DCA penalty box to take off.

RRDD

I'm still confused as to the real policy, but DL gave me 7500 miles when my short flight went out with one empty FC seat and me 1 of 1 on the upgrade list.

"Thanks for reaching out to us. I definitely understand your disappointment when you didn’t get the First class upgrade even though you were first on the upgrade list. I note that our attendant didn’t come to move you to First class. I can realize your displeasure as the flight left with one First class seat open. This is not what we want our customers to go through. I’m really sorry you didn’t get the service you expected and deserved. Your feedback is important to us. I’ll be sure to forward your comments to our Airport Customer Service and In-Flight Service team for their internal follow up."

xliioper

This seems to have been pretty well covered at this point and the "official" policy is that GA's have discretion to move up those already boarded, but only if time permits. In other words, there are no absolute guarantees here. If you are number 1 on the list, you should always ask before boarding if FC has boarded full and if the GA will come and move you up if there are no shows. If you do that and they fail to move you up after saying they will, you have grounds for a complaint. I've had some cases where they have told me to hold back while they wait to see if there are no-show's. Obviously not ideal when you have overhead luggage you want to stow, but if they are short for time I don't think it is entirely unreasonable to ask you to wait.