A-Body Door Jambs Different

I ordered a new drivers side amd door jamb panel for a plymouth duster I am working on. What was weird to me, on AMD's website the door jamb panel is specific to the duster/demon only.

Now we all know that the dart and and scamp use a very similar door except they have the triangle window in the front. My question is since the doors are the same what makes the scamp and dart door jamb different? Same door same door jamb is what i assumed but apparently there is a difference.

Also I should mention I am referring to 2 door darts. 4 door cars have a different door jamb.