Naturally they had problems if they wrote it YY/MM/DD. It's not a correct way of formatting the ISO 8601 date. It's supposed to be YY-MM-DD. If you use slashes between them it can be just about any format but if it's minuses it's YMD.
The full year is required to make it clear that 23-12-10 isn’t the day before X-mas eve in 2010