Like I said, 1 day of separation doesn't seem like anything remarkable, but it begs the question: do the numbers get reused for the same flight on shorter intervals than a day? If so, when? Even more interesting, why?
And, technically, the two flights 1555 in my example aren't the same - one departed at 4:00, and the other at 4:20. Both flights were on-time, so this wasn't a scheduling issue delaying one or the other. 20 minutes isn't a big difference, but it is still a difference. How big does the difference have to be to make Southwest assign two different codes?
Even more philosophically asinine, what do we even mean when we say two flights are "the same?" If Southwest thinks those two flights are the same, then clearly departure time only matters within a certain fudge factor. So that's one part of the picture. Do the make and model of plane need to be the same? Does it need to be the very same physical airplane?
Are any of these questions important to my everyday life? No! Are they interesting? Absolutely!
I've seen situations in the past where the same flight number referred to multiple flights between endpoints that had no apparent relationship to each other. I've also seen a single flight number refer to a flight from A to B to C, but used a different aircraft to get from A to B than from B to C. I can't find any examples at the moment though so maybe the airlines have stopped that particular insanity.
Also, airlines regularly make minor tweaks to their schedules. It's possible that what you saw was one of those tweaks taking effect.
And, technically, the two flights 1555 in my example aren't the same - one departed at 4:00, and the other at 4:20. Both flights were on-time, so this wasn't a scheduling issue delaying one or the other. 20 minutes isn't a big difference, but it is still a difference. How big does the difference have to be to make Southwest assign two different codes?
Even more philosophically asinine, what do we even mean when we say two flights are "the same?" If Southwest thinks those two flights are the same, then clearly departure time only matters within a certain fudge factor. So that's one part of the picture. Do the make and model of plane need to be the same? Does it need to be the very same physical airplane?
Are any of these questions important to my everyday life? No! Are they interesting? Absolutely!