Look at it this way: the running from Euclid to 205th is still a for the majority of its route. If you truncated that service to just run between 145th and 205th, that isn't really the anymore, even if the majority of folks know that the is replacing service along the Concourse.
I know it seems counterproductive to call the overnight shuttle a "", but it's the most effective way at differentiating the day service where trains from the Bronx are still running into Midtown and Brooklyn, and night service where trains are only running to/from Harlem.