The term was derived from a "dutchman's repair" where a piece of cement would spall and dip causing a deformation in the stone.
A Dutchman repair, involves the cutting out of the damaged stone keyed sides. A piece of new stone is then prepared to fit into the slot.
Translating that to the automotive world, it was much easier to add an extra panel to the back of the vehicle rather than form the body as it slopes up to the roof from the trunk while trying to form the curvature on the side of the body as well
