Why is this date format used and where can it be used?
DateTime date1 = new DateTime(YY, MM, DD);
DateTime date2 = new DateTime(YY, 4, 1);
DateTime date3 = new DateTime(YY, 12, 31);
DateTime date4 = new DateTime(YY, 3, 31);
DateTime date5 = new DateTime(YY - 1, MM, DD);
DateTime date6 = new DateTime(YY + 1, MM, DD);
DateTime date7 = new DateTime(YY, 1, 1);