I’ve had this very thing happen. I asked the “senior” pilot if he could also list as a non-rev. He said he tried but it didn’t work. Whatever. He was on “the list.” We both got on in the jumpseats.

Had another time, (not on UAL but on DAL), where I was the only JS listed. I get to the gate to check in and gate agent told me there was already a JS checked in. He was deadheading but since they were trying to get one more passenger on, he asked him if he would take the JS instead. He happen to be standing next to me so I asked if he could take his seat instead so that I could get the JS. He literally shrugged, took the Jumpseat pass the gate agent was holding out to him and walked down the jetway. Told him thanks as he walked away. Don’t know if he was on the list since I didn’t get his name but I doubt it since he was young.