I'm not sure what your question is, so I'll say a couple of things.
When Clark Street is closed, the runs express along Lexington Avenue and only Lexington Avenue (assuming no work knocks out one of the local tracks in Brooklyn or the Bronx). Since it covers quite the distance (or short-turns at Grand Central or 86th Street) and serves as a third overnight route under these circumstances, it becomes the night express.
Under normal circumstances, and trains run their full routes as overnight locals, whereas the is short-turned at East 180th Street (no Manhattan service). During the day, the runs local on its full route, the runs express in Brooklyn and Manhattan and short-turns at Utica Avenue, and the runs express in Manhattan to Bowling Green. It wouldn't be hard to imagine the becoming an overnight express to Bowling Green, but the will to run it isn't there...