He knew how in his youth. Seems to have stopped sometime after 1918, although I have seen him with a full beard as early as 1909 . . . Z
Could it be that the hub (the master image from which all of the working dies are are made) is wearing out again? That happened between 1909 and 1968 In 1969, the hub was re-done. I would say that it is not a hub problem. Back in the late ‘90s, the mint went on a campaign to give the portraits on our coins a lot more detail. Collectors who didn’t care for that all that much gave the revised designs derisive names like “spaghetti hair.” It was most noticeable on the Washington Quarter, but all of the coins from the period had stronger defined hair detail. "Spaghetti hair" Washington Previous Washington I believe that Lincoln got a make-over during the the "spaghetti hair" period, and perhaps that is what you are noticing.