I have one specific question, counting on an expert answer here:
Can an air traffic controller licensed for one location issue approach clearances for multiple airports in his airspace?
For example, let's take Westchester County Airport, New York (near La Guardia).
AirNav: KHPN - Westchester County Airport
As stated on that webpage, approach service is provided by New York Approach (120.8). That's one of the La Guardia frequencies. Obviously, that controller in New York Approach should be licensed for La Guardia and has something like "KLGA APP" in his ATC license. Should he also have something like "KHPN APP"? Or KHPN is somehow implied in this case?