The first image looks more like a generic rear plate but it could have holes on the top surface from a WD rear light and contract plate.
If this is the case then perhaps oddly it has the mounting for the rear lamp on the continental side.
Jan and I have been noticing this on machines of some makes apparently supplied to some European markets during the late 1930s. It's not yet clear whether they were fitted as original to some early-war contracts for friendly European military authorities.
We need to find some Dutch and French contract parts books.