I'm not convinced about the limited amount of wear having much infuence on the interiors of the "8" or "9" even allowing for the inside edge to be slightly bevelled - images of similarly worn coins appear to have larger interiors and I have not ( in ten minutes) been able to trace any currency examples with an 8 or 9 similar to Bruce's specimen. However, an 1879 proof does seem to have slightly thicker 8s and 9s to currency examples. In Bruce's specimen, the "7" is also thicker than normal, but some variety in this character does exist in currency specimens, so why not thicker 8s and 9s. Perhaps useful to check the size and weight of the coin.