That’s great, Jakuje, thanks a lot – exactly what I was looking for. So simple, and I never tried ...
@ pinkunicorn: yes, indeed, but that’s just what I wanted to say, i.e. that those old caches do not have a publish date (log), so the first log is simply the first logged find (or DNF). I don't think there is any way to know when those old caches were published. (Other than between the "hidden date" and the first log, be it a found or DNF.) Or is there?