Putting the year first makes it unambiguous. Some places do month-day-year, and other places do day-month-year, so any date up to the 12th of the month can be c

Putting the year first makes it unambiguous. Some places do month-day-year, and other places do day-month-year, so any date up to the 12th of the month can be confused. But if the year comes first then it's always year-month-day. Also, a 4-digit year is important here.