The reason for the found date tool seems to be the possibility to generate a ICS File:
Generate a calendar reminder to go out caching on days without found.
Thats for the reason to not have to wait another year (or 4 in case of 29. Feb).
There is no reason for a "reminder" to hidden dates...
Of course map based tool can also handle additional Filters. Map compare allows to set specific hidden dates - but unfortunately not for a specific day in all years.
As mentioned before you can take a look into your profile to get an overview:
Uhhh, your calendar is full :-0