> It makes zero difference to the movie watching experience if the script line came from the script or the other way around. While you’re watching the movie, the effect is exactly the same.

Certainly not true in the case of a work adapted from another source like a novel. The words "The Fellowship of the Ring" are never uttered in The Fellowship of the Ring, and Peter Jackson's ham-fisted insert there was obvious even to people who hadn't read it, but especially to those of us who have.

And, by that token, if the dialogue suddenly seems awkward and stunted for no other reason than to insert the title, most people would probably conclude that the title came first.