I think that that is mechanical/machine doubling. It's pretty common and not worth much of a price increase, if at all.
MD is when the coin gets a little loose in the holder, however minor. In the millisecond after the good strike, the die will move a little in one direction or rotation as the die rises up off the planchet. It will leave what is called a shadow or shelf-like image of the design on one side of it. Depending on how loose you can get a good shadow/shelf, but sometimes just a little. Once a worker tightens the holder, no more MD. On some dates/denominations it's not uncommon
1969-S DDO does not have doubling on the mintmark. At that time mint marks were applied to working dies not hubs.