At some point we discriminate between two still authoritative narrators, and we always distinguish them from the unauthoritative. Be "we" I mean "me."

This is true as an observation of human behaviour, but ultimately I don't know why we have to do this - that is, I can't see any reason to label one the false god, one the true, beyond a kind of neurotic urge to have everything neat and hierarchically tidy. If we were interpreting laws in a court there would be a point to it, but it's not obvious what the point is when we're talking about something as irreducibly multiple as story.