Do Greyhound buses from NYC to DC depart from Port Authority or do they depart from the Greyhound station near the George Washington bridge?
This is a bug in the address details on Greyhound.com.
Greyhound's main station in New York is still Port Authority Bus Terminal.
Greyound.com treats each stop as a "city." The "main" stop is the city: New York, NY is Port Authority Bus Terminal. If you want to depart from secondary stops like George Washington Bridge (or Brooklyn) you need to choose them as the search origin: e.g. New York GW Bridge, NY:
Searching for New York GW Bridge, NY you'll see different buses than those from New York, NY, prooving the results you're looking at aren't for that station.
At Busbud our searches return all stations in the city. You'll see we differentiate between the two stations, and that the vast majority of buses leave Port Authority like you'd expect. We're leveraging the data we're getting directly from Greyhound.
Selecting an itinerary on the Greyhound web site for your desired city pair will allow you to see the location of the bus stations involved.
For example: Click View Itinerary, then place your mouse over the name of the city, and the terminal information appears:
For all the schedules I looked at, it appears that all of them depart from the GW Bridge terminal. I could not find any departing from Port Authority from a quick look around.