The reason it doesn't show MD on the other areas it that the mintmark was set deep into the die and is taller than the other devices. If it had been a lower bounce would expect to see MD on the other devices.
So lets look to see why it is
Machine Doubling.
First off is the mintmark enlarged with that affected area? No. The mark is incuse. If it were a RPM, then the mintmark itself would be larger. Take a look at the RPMs for that year on V.V:
http://www.varietyvista.com/09b%20W...201964-D.htmNote they are showing an enlarged area on each on. Note they are all N, NW or South that year. So the mintmarks are all taller than normal. If you checked blike on the highest areas of the eagle or bust, you might find some
Machine Doubling?