That is die wear. The devices tend to show wear in the direction of the closest rim. If it were a doubled die, then all the devices would be affected the same. They are not. Note on the other side, of the EPU, you see the same thing, but in the opposite direction. These devices are moving to the right to the closest rim. Machine Doubling
is also present on the right side devices. Sometimes this is die wear, other times it is hub wear. Thus a lot of quarters have a distorted motto issue on many years. The way you can tell if it is common, then all the coins will appear the same if it is a master hub issue. If it is a working die issue, you will see several examples, but on the pre 1990 coins, the mintmarks will be in different locations. Down the chain of command:
Note only one Master hub is created. So if something is wrong with it, all the coins will show the same thing.
Next step down. Master dies (2). So if there is doubling there on one master die, 50% of the coins will be affected.
Working hubs, if one is affected, many dies can show the same issue. But not all or a large part of the coin will be affected. So the issue can be total, or half of the coins affected or sections of the coins affected. Die variety collectors prefer single die doubled dies. Those are the more rare ones. And Proof doubled dies are even rarer as the amount of coins struck by them is 3,000. So the prices will be higher as there are less of these out there. But the common normal proof coins are less in demand for them. (Even graded prices show how low the values for these are)