I remember reading about this in a web forum mainly for dublin core fanatics. Metadata is fascinating.

Different software reacts in different ways to partial specifications of yyyy/mm/dd such that you can try some of the cute tricks but probably only one s.w. package honours it.

And the majors ignore almost all fields other than a core set of one or two, disagree about their semantics, and also do wierd stuff with file name and atime/mtime.