How to find earliest date and set all dates to this value ?

[gepardieu]

Hi, I have a large number of images and videos which all have different sets of date values, most of which don't match.. I would like to conditionally for each file find the earliest date, whether it is the DateTimeOriginal, FileModify, MediaCreate, GSPDate, etc., and set all dates (or at least set the DateTimeOriginal) to this date. This would include to first remove all dates with zero or 1904 values . Can this be done e.g. using conditional expressions in exiftool? Thanks in advance

[StarGeek]

This would best be done with a user defined tag.  See this thread.