Only on DL

Last Feb, I flew in paid F on ATL-SFO on DL on a Friday midday flight, F was sold out a few weeks in advance and remained that way pretty much until boarding. The list was over 40 deep with 24/24 seats checked in. We boarded, turns out there were a couple of misconnects and the flight closed with 19/24 seats occupied in F. Not one single person was upgraded, because they boarded the flight rather than waiting over at the podium.

While it may seem less disruptive to the boarding process, it is undoubtedly more disruptive to the GAs. I have seen many situations where there were several Diamonds hovering the podium distracting the GA over 1 or 2 open seats and the others constantly asking in hopes of no show. DL GAs does a pretty good job of being patient and answering the same question over and over again, but I can see that they want to focus on getting the flight out on time.

Having UA's SOP where everyone boards irregardless of the F cabin availability then the GA can run the upgrade and being down the BPs along with the final paperwork to the plane. They know who is onboard and those on the upgrade list who didn't board would have been offloaded and thusly removed from the upgrade list automatically. In this case, sounds like the GA processed the upgrade first before offloading no shows.