That's weird, the most common behavior is every SDL variable being local to the Age it's from. There is an exception with Ahnonay which uses yet another method to sync the current active sphere in CC, but that's not the case here.
It may be related to instancing - sharing SDL stuff is the sort of thing sub-Ages (or child-Ages, I don't remember) are for. However, I don't recall seeing the D'ni locations as sub Ages of the city or the GZ.
According to the Offline-KI, the GTP is a public link. And it doesn't seem to be related to server-rules since it applies offine too.
Or it might mean somehow SDLs can be made global to the whole game - which could explain why every SDL variable begins with the Age name, so that we know from which record they are from.
I doubt that's the default behavior, though. At some point I used two identical variable names in two Ages, and they were never in sync (which I verified just now).