The fundamental flaw in any sort of cutoff (whether it be 24 hours, 72 hours, even 6 hours) is that it doesn't take into account day of departure operational issues.

Was there perhaps an AUS-IAH flight with 10 BF pax flying AUS-IAH-LGW that got severely delayed leaving AUS and missed IAH-LGW?

What about someone flying DEN-IAH-LGW in BF who got bumped in DEN and rerouted DEN-EWR-LGW?

What about the person flying MEX-IAH-LGW in BF who got stuck in a long immigration line in IAH and misconnected?

What about someone who changes his ticket on the day of departure to fly the next day? Or cancels it altogether?

All these scenarios, which are reasonably common, can impact availability on the day of departure. But the waitlist system (in its present form) does not allow Elites/upgraders to upgrade when space opens up at the last minute.

I can't speak about the 6 gate upgrades, I'm sure CO Insider can look up what happened there. But fundamentally, the problem is that someone wants the seat, is willing to pay for it (albeit in miles in this case), inventory management did the best it could (up to the 24 hour mark), and let's face it, either they don't get it 100% right every time and/or things happen on departure day.