I noticed, after some tinkering, that if you spawn at a new airport you are more likely that your airport will show up in that list.
if you terminate the connection to SimConnect (while leaving the sim up) and reconnect, you get that basic 1243 again…
You can repeat that cycle over and over.
Going back to main menu, spawning back at that same airport doesn’t get you the list with your airport in it either, its only on the “first” load to that airport.
I’d expect that the subscription would return all the airports or N of the ones closest to me.
I tried slewing around the area after loading in, and the subscription works, but I don’t know what the cutoff is for its search area to return new airports.