This coin was struck through grease that was on the die causing the certain details to not appear. There is some value associated with this error the more severe the grease strike, but this example is not that severe. Here is a link to a site that goes more in-depth on this type of error: https://www.error-ref.com/grease-mediated-radial-smear/
Not sure about struck through grease. Looking at the overlay from maddieclashes.com the missing letters and date may have been caused by the flow of metal during the strike filling the letters UN and RI on the anvil (reverse) die. Overlay from maddieclashes.com
