Sure, that's one factor. (In theoretical linguistics there's a big literature on it.)I think that's just a basic problem with English. If I say "I have a dollar in my pocket", there's no way to parse whether I have "exactly" one dollar or "at least" one dollar. Same thing for "Oerth has two moons".
But there's a broader issues too.
Some descriptions present themselves as implicitly complete, at least in certain respect - eg if the GM says "You see a mouse and a treasure chest" that is consistent with the PCs also seeing a huge red dragon, but the description implicitly precludes that, because the visible presence of the dragon would be so overwhelmingly salient in contrast to the mouse, and in the context of the chest, that for the GM to omit to mention it generates an implicatioin that it is absent.
On the other hand, "You see a mouse and a treasure chest" also leaves it open that the PCs see some dust on the floor and some damp patches on the walls. (This is what many of the "gotcha" monsters trade on.)
To me, the idea that the description of the Celestial Bureaucracy in OA leaves it open that's it's just a minor municipal operation in the context of the grand Faerunian pantheon and cosmology - such that placing OA into the FR is addition, not change - yet an explicitly in-fiction account of the visible heavens precludes a third moon that is invisible to the naked eye, is ridiculous. And my inability to reconcile them is not based on concerns about parsing sentence of English. It's about communication and salience, about what is implicitly precluded or left open by one account but not by the other.