1968 Nickel Dollar: PL DDR Or MD?

Yes ... I fully agree with you. What you have described to me is the definition of "hub doubling", which is prevalent in some of the Vicky large cent years that I collect. In Alan Herbert's book on Errors, he describes eight different hub-doubling types, split about half and half as caused by deliberate changes or machinery/pressure problems. For years, I have essentially described those caused by machinery as "die chatter" (the working die slightly moving as it is being struck by the hub while making the working die). Only in the past few years have I even seen the annotation of DDR and DDO to define what I always called "hub-doubling". The minor differences (offsets) seen by and caused by the 2nd, 3rd or 4th strikes of the hub striking/making the finished working die, either by chatter or manual (rotational, offset, pivoted, or tilted) look to be what affected the 1968 mintings. Maybe specific terminology differences or verbiage have distorted what "doubled die" all entails and now means with the moniker DDR or DDO. I prefer to use the old terms of hub-doubling and use DD as intentional repunches.