But you will admit that the matter is strange. Luggage vehicles ok, catering vehicle ok (the service door is at the same height as the cabin door) but the stairs did not work.
Why "strange" ? I already explained it here:
You say you are missing the front stairs, so they are affected by the front door. Baggage loaders are affected by the cargo doors instead so, fact they work, would only indicate the cargo doors are correctly configured, which doesn't exclude the front door might not.
So, it seems in your case, the only door missing was the front one.
Also, as I've said, GSX already has an internal configuration for the Maddog, which will be active if the airplane folder is named MADDOG2006, MADDOG2008 or MADDOG2010 so, either the new version ( which I haven't seen ) use the same names, so you started with the default GSX configuration for the Maddog (which DOES disable the front stairs, since the airplane used to come with its own), or the plane already comes pre-configured with a GSX.CFG file that was made that way.
Again, the GSX airplane configuration WILL tell you from where the GSX is taking the airplane configuration data from so, if you checked it BEFORE you starting to configure it yourself (now, it obviously saying is using YOUR own configuration), you would have known from which kind of data you were starting with.