Sometimes it's automagic, sometimes there are wonderful people behind the scenes making magic happen. I know at least one airport where premium services agents will look at elite (or at least GS/1K) PNRs when a flight is trending in a sideways direction and insert protection manually.

Last year I nearly had a heart attack because there were two ORD delayed flights -- the one I had booked, (delayed by a few hours) and an earlier one that was now delayed to around my originally scheduled departure. An angel had moved me to the earlier one without be realizing until I was half way to the club and looked at the boarding time on my BP -- which was about 20 minutes prior to the current time.

Sopped by the club thinking I was just going to give them the BP scan because I had horribly misjudged my morning and would be lucky to make the flight... when it was pointed out to me that my itinerary had been "adjusted", that flight was delayed, and I had plenty of time for my heart rate to come down. And just in case the original segment was left intact as protection

And this is why I love "my" agents.