But what is really strange, is that RMBT rates 143 SH6. Means 12-13 coins seen, scarce but not rare. 
That was also puzzling me about the considered rarity vs real market rarity. On the other hand we might safely assume that the main reason why we don't see them often is that being desirable, collectors are less likely to part with them.
About the appearance. Maybe it was a harsh cleaning or even a bit of tooling and smoothing involved?
