Found this nickel today. . Looks like it was smashed. . The obverse has bottom half smaller, dime size. The reverse top half dime size?
It looks like it was either smashed so small it is no longer visible to the eye, or you forgot to post pictures.
I acknowledge that I am still learning, but the dark line on the reverse looks like the place that the metal "hinge" of the lamination would have been. The strike gets more blurry towards the rim because that metal didn't transfer the design well. Eventually, the metal flake that used to be there came off. That is my theory. I look forward to other responses.
Looks like it was partially dipped into some corrosive liquid and suspended that way for some length of time before being removed. PMD.