1972 Duster Org. paint Resto detail

Hey guys, thought this was very interesting. Bule 1972 duster, paint is factory. Notice the bottom attachment point for the front fenders. The small square attachment point is painted black. it is painted with a brush. I have done many resto on b and e body cars and don't recall ever seeing this. I would assume that only light color paint would receive. I know across the board that this bolt would be black phos. Any other members car like this? How could i have miss this all these years? Is this an A body thing only? Car is a Hamtramck plant car.