I’m using gramps 5.1.3 and I experienced a problem (at least in my view) with the filters.
The general idea is to filter persons who (1) are born “before 1928-05-01” AND (2) died “after 1920-02-24”.
I used these two rules and in filter settings I selected the option “All rules must apply”.
So a person which is for example born 1924-03-04 and died 2010-11-16 should be visible when applying this filter. Unfortunately this didn’t happen. From all the persons for which the rules match only a smaller sample of persons were shown. But I can’t figure out why the other persons (which fit the rules, too) aren’t shown as well.
I created a clean new “John Doe” which was born 1900-01-01 and died 1950-01-01. This person is shown when applying the filter. So I can’t reproduce the problem with the new “John Doe”.
In Gramps, the terms ‘before’, ‘after’, and ‘about’ are defined in Preferences (menu >> Edit >. Preferences). The default is 50 years.
In your filter died ‘after 1920-02-24’ the filter rule is actually only out to 1970-02-24. For the ‘before 1928’ rule it looks down to 1878. FYI: the ‘about’ is +/- 50 years from the date used.
In your example, to get the desired results use ‘between 1920-02-24 and 2023-02-02’ and ‘between 1000 and 1928-05-01’.
When the modifiers are applied to an event date; died ‘before 1980’ this person would have returned as valid for your original filter. Gramps would evaluate ‘before 1980’ as between 1930 and 1980. Since this would be true for your filter looking for dates out to 1970 it would return as true.
NOTE: The ‘before’ and ‘after’ limits do not apply to dates used to set up the Place database hierarchy.
Personally, I reduced the limits in Preferences down to 5 years. This primarily for when a filter would return them as true. Regardless of filtering by date, it is always best to use ‘between <date1> and <date2>’ instead of ‘before’ and ‘after’.
Your new John Doe fell within in your original filter as true. He died before 1970-02-24.
Thank you a lot for your detailed answer! This explains a lot! I modified the filter according to your advice and it works great!