@Scrappy and all of us here. This it is not Machine Doubling
, it is an accepted deviation of the Die production.
MD by definition is when the anvil or the hammer move. On those bi-ball presses the Dies could not move laterally, if move the line stop. From the introduction of horizontal striking presses bi-ball first generation in 1999 the term MD and feeder fingers do not exist any more. I will explain: I put 4 time the Mint film of striking and 2 time how the modern dies are produce. Seem no one take attention on.
This coin is not an error and no variety. The error could be an DD which has backbone in the re-engraving the master die, and if discover in essay will be destroy. We can have other errors of production but I will not enumerate here (in fact only 5 kind could be find from tome in time). Varieties are considered any changes of design or intervention which change the design.
Why this coins show this: when the Die (anvil or hammer) is done in the case of Quarters are 4 pressing steps. First is very high pressure slow then followed by 3 others in orders very fast. Some times the last strike have 't a small rebound from the previous pressing and this can cause this effect only on some locations. This is normal no error, it is what it say: Production parameters.
For collectors, and all I know they know very well what is in parameters or not is not considered more then a 2nd quality of minting. Some dealers and speculators will advertise like big error.
An extra: Feder Fingers: Do not exist on those presses. The Blanks type2 or planchet how you want to say: on those lines fall direct in the collar. The line of collars is round way. So the blanket fall on horizontal in the collar, and before to take the vertical side of the collars chain is press by a ball, fixing in. some times some off centers could happened and is normal for a speed of 750 coins a minute.
Hope help everyone.