I worked on a system once that failed in Sweden when we changed the locale from US. Someone was getting the date as 01MMMYYYY and using it as a partition name.

I worked on a system once that failed in Sweden when we changed the locale from US. Someone was getting the date as 01MMMYYYY and using it as a partition name. When the first day of the tenth month happened, everything broke, because it was expecting OCT, not OKT. Unambiguous but wrong. With humans reading it, either you need to be unambiguous, so use yyyy-mm-dd, or you don't have to be, so use a format that most of your audience will understand.