I flew the "type" for 11 years; MD-82, MD-83. The designation on my license says DC-9. When you get "typed" in the model of jet, that ended up off the runway in Goma, my license does not say MD-80 but DC-9. At least that was my experience here is the USA under the FAA.
So, I would look at the pictures above labeled DC-9 and interpret that as the appropriate designation. Yes it is a MD-80, but I suspect an inspection of its type certification would reveal a DC-9; as all subsequent derivatives of the model trace their certification to the DC-9 designator.