The year 2001 is the first year since 1931 when a 2-digit year could be confused with a day of the month.
It's the first time since 1912 that a 2-digit year could be confused with a month.

So, what is "01/02/03"?
Is it January 2nd, 2003, February 3rd, 2001, or something else?
''(Six possible interpretations.)''
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I recently encountered some code that tried and failed to convert "YY/MM/DD" data based on a "MM/DD/YY" format, from 1995 to 2000.
Ironically, it always produced the correct result, because its error processing always silently reverted to the previously formatted data, which was correct.
Now that "01/01/17" (January 17th, 2001) can be interpreted with the "MM/DD/YY" format (as January 1st, 2017), the program produces incorrect results... starting January 2nd, 2001.
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See also InternationalDateFormat.
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CategoryBug