Actually, the next station east of PMJ is Lake Hopatcong.  Hackettstown is farther down the line on what would be a separate branch of operation for NJ Transit (trains to and from the Cut-Off will not pass Hackettstown).  You raise a valid point, however.  We don't know what NJ Transit will call the Cut-Off and the extension into PA.  Technically, it would be correct, at least at this point in time, to call it an extension of the Montclair-Boonton Line.  More detail on this would help, as would a map.