I don't know why I would, but if I were going to sandblast a coin the first thing I would do would be to figure out a way to hold it steady so the blasting would not just slide the coin away. I think the first thing I would try would be to bore a shallow dime size hole in a piece of wood to hold it, do one side then flip it. I guess this would also protect the edge from the sandblasting. That being said, I don't see anyone spending that kind of time on it. I believe it is simply environmental damage. There could be any number of reasons the edge was not affected, or it may have been smoothed out afterword from friction or handling.