I was booked on the LGA-DCA Shuttle yesterday as a PM on a full Y fare (my upgrade cleared at the window last week, not at booking which I thought was odd, but I digress).
I SDC'd to an earlier flight and the GA told me she couldn't process my upgrade then, but that I would go on the upgrade list for my new flight - fine with me. I boarded with Sky for my C+ seat and the machine spit out a new seat in F - great.
F was relatively light after boarding was finished so the GA came on to pull people up front, including a man with a shiny DM tag on his bag.

I've been trying to figure out how he could have been in the back while my upgrade cleared at the gate. I've come up with two scenarios, but I'm curious if you all know of anything else that could have happened, maybe a rule that I've forgotten or something...
1. He bought his ticket as a walk-up after the GA had cleared all the upgrades at the gate (had to have been a narrow window for this to happen and he didn't seem like he had been in a rush)
2. His DM tag was leftover from last year and he's actually now a PM or below. But that would have taken effect in March, so surely he would have removed his tag by now?

Any other ideas?