The SFO-DEN-AUS flight (~3:50) was after the SFO-AUS flight (~2:20). I was at the airport around 11:30 just within the 3 hour same day confirm window, and this was when I was talking with the RCC agent. I suspected SFO-DEN was likely to be VDB because it was F0 Y0 and the agent confirmed it was indeed planned for VDBs.

I'm not complaining ($100 < $150, but for $150 I would have likely done standby rather than pay - so maybe it was a very smart price after all). However, the way the fee was done and then not being able to explain it was, well, just weird.