If you are creating a relationship between times in the past, you have to convert from string to something else. And the something else is always subject to som

If you are creating a relationship between times in the past, you have to convert from string to something else. And the something else is always subject to some other detail - the calendar of the past is not defined identically throughout history, so you can't just extrapolate year-month-day backwards to get a time. Nobody's really solved this, it has to be tackled anew for each case of "comparing dates from long ago".