Heuristically, "if it has slashes, it's USian mm/dd/yy, if it has dots, it's European dd.mm.yy, if it has dashes, it's ISOish yy-mm-dd, YMMV."
Heuristically, "if it has slashes, it's USian mm/dd/yy, if it has dots, it's European dd.mm.yy, if it has dashes, it's ISOish yy-mm-dd, YMMV."