In an earlier post the Op talked about coin attrition and alluded to maybe others not yet found, being in a collection, an unfound hoard, etc. There's always another hiding out there somewhere. This was found by a collector in garden City, N.Y. It's being attributed by PCGS as BB126 with different obverse and reverse dies. The whole story is at Numismatic News.
I believe this will not be an isolated case. I think other rare coins will come to the market as the octogenarians pass away. I don't think they will found in any great number, but logic tells me there are more out there. They are just tucked away at the moment.