Tempest, This is only an opinion. I am not an authority. Notice the uneven-ness of the rim area? It seems to be "puffy". which , (IMHO), is caused by the upset mill, "crushing" the edge of the planchet. Then the striking process causes it to be struck sooner than the rest, by a nano-second, leaving an impression of the die. Then the full "weight" falls, and the full impression is then transferred. The final thought is that the "early striking of only a small area, (like maybe only two letters), will cause more wear in that area of the die, because of having already srtuck, momentarily. Crude at best, but that is what I believe is the cause, or one of the causes of this anomily.
Dick