I think you misunderstood the earlier post. When a movie is filmed it is shot on 35mm(4:3) and then the top and bottom can be cropped(assuming it wasn't an anamorphic lens). In that case there is material on the top and bottom that could be used depending on anything too problematic showing. For a TV show that is originally 4:3 there is no extra material. On occasion there might be some material that was cropped to zoom in a little, but on most scenes there is no extra material to use. To make the image wide screen you must crop off the top and bottom.
Do we know for sure that the entire 4:3 frame was used? The reused ten-forward sequence from "These Are the Voyages" would seem to suggest that the videotape transfers were cropped from wider shots. That extra information off to either side of the replicator has to come from somewhere
Now whether this applies to the show as a whole or in only a few particular shots is not certain. Can we get the TNG editing staff in here to comment?