I may be wrong, but I think that the ASE's with milk spots come from the mint that way. I don't know if a coin can develop milk spots unless maybe someone sneezes on it or spills something on it ???
Yes and no. The milk spots are definitely caused by whatever it is that happens at the mint. But they do not always show up right away. You can have the coin in your possession for months or even a year and THEN have the spots show up.