I think it's better to just say "it's an oversight" than to rationalise like that.
I disagree. I think there's a silly tendency to assume things like *the first time anyone ever said the name Elturgard was the day Elturgard was officially founded via source book text. Any mention of the word Elturgard before that was an oversight.*
I have zero interest in that line of thinking. I imagine that Elturgard was a dream rolling off tongues long before it was first drawn on a map.
In my opinion, there are a couple of approaches to this sort of thing we see. One approach comes from a group I would call "students of source books." The other approach comes from a group I would call "students of human moves."