I recently flew STT-ATL and was #5 on the upgrade list with 0 seats available. I figured it was a non-starter so didn’t bother monitoring the list, but after I boarded, I happened to look in the app and 1-4 had all cleared, leaving me at #1. Any idea how/why this might have happened? If I had known I still had a shot I would’ve used an RUC to move higher up on the list.

No shows most likely. With no change fees and the like there has been a significant increase in no shows as you automatically get a credit back. That said, I'm surprised that this would be the case on STT-ATL as those trips are typically booked round trip originating from the US meaning that the return leg would also be cancelled upon no showing.

Could also be that the gate agent forced (or negotiated with) families / couples to sit together which opens up more seats given the seat blocking. One family of four will take up the entire left side of a 738 but could consolidate into two rows, leaving up to 4 seats free if the next four folks on the upgrade list were couples.

Was the flight full / oversold?

Could be no shows, SDCs/SDSs, missed connections, etc. No shows are more likely than before since there's no penalty or requirement that segments be cancelled before departure to get either a voucher or refund for a ticket.

It's good that the GA bothered to do (his/her job) upgrades at the gate.

Applying an RUC doesn’t means it gets used unless it actually clears. You could have thus applied it which would have put you higher up on the list that if any seats cleared you would have had the seat.

I've noticed that the seat availability on the UG list doesn't always accurately reflect the true count due to the fact that couples no longer count twice against a 50% cap. This is likely the case on a route like STT-ATL.

When I flew DTW-ATL a couple weeks ago, the app showed 1 seat available but there were actually 3 as there were two couples in FC. I can usually get a better idea of available seats by simply counting the number of empty pairs on the seat map (although be aware that 1C/D are blocked on certain aircraft).

100% true. The only reason I didn't was because I hadn't yet selected them as my choice benefit, and didn't think it was worth it to "start the clock". Boy was I wrong.

This probably would've worked in my favor, too. Based on the matching last names in the app, it appeared that the 4 seats were actually 2 couples. So maybe it really only took 2 no-shows to free things up.

Yes, the no-shows/SDCs seem pretty plausible. It was the first flight of the day, and with customs and Delta's 90 minute check-in requirement for bags (the longest I've ever seen) it's very easy to run into trouble at STT if you don't arrive on time.

STT-ATL is a short flight. With the terrible F service these days I think you made the right call by not pulling the trigger on RUC benefit and starting that clock. Save those future RUC's for longer flights when service is something more than cheap wine and garbage processed food snacks.

Not directly related to the topic (though perhaps the cause for the seats becoming available) but I learned something today and that is that you are required to go through Customs when departing STT, even if on a flight to the US. I never knew this.

i was surprised the first time too. And that was on a flight from STT to SJU. FWiW I asked and was told it was that STT was some sort of “possession” while SJU was not.

At least in the United States, territories and possessions are interchangeable terms (both Puerto Rico and the US Virgin Islands are both territories and possessions). The difference is that Puerto Rico is part of the same customs territory as the 50 US states (and Washington D.C.). The USVI, Guam and the Northern Mariana Island are all independent customs territories.

This is more about customs (i.e. taxing of goods) than it is about immigration - although since the USVI essentially "contracts" their customs enforcement through CBP, the CBP will never skip a chance to do a "papers please" which is why they require proof of citizenship (passport or drivers license + birth certificate) upon exit.

I did STT-ATL back in December and a passport or birth certificate was not required.

CBP is typically fine with a Real-ID complaint drivers license as well. Again, the stated purpose of the customs exit is for customs and not immigration. But they'll pressure you to present a passport and/or supporting documentation if they feel like being obnoxious. Here is the CBP site giving the lovely "double speak" that while it is not required, it is "recommended".

I've been detained for 9 hours at STT before because I legally refused to provide a passport or proof of citizenship. They eventually let me go (right at the 8-9 hour mark where courts have delineated the end of reasonableness for an "administrative hold" whereupon the CBP must have reasonable suspicion to hold someone further) but my point is, the CBP will go through a papers-please motion if they feel so inclined.

I obviously missed my flight and had to stay an extra day. I went back and they held me another 2 hours before they finally let me fly home.

I had a flight RSW/MSP on December 8 2020. There were no seats available (in first class, even for purchase), even upon arrival at the airport. I had some RUC's that were expiring, so
I applied one for a waitlist, just for the heck of it. About 30 minutes prior to departure, I cleared the WL as did four other people. I think it likely had to do with the "renumbering" of
people traveling together.