sgarfield posted a comment on discussion General Discussion

The format used by xml2biblatex for providing dates in biblatex is incorrect. biblatex does support "year" and "month" (mainly for legacy reasons) but not "day". The correct form is to use a "date" (or "origdate", "eventdate", "urldate") field, and format its content according to ISO 8601, a.k.a. EDTF. Using a "date" field is preferred even if a date consists of just a year, or year+month. Dates, date ranges and date/time combos are supported, e.g. 1850 1997/ /1997 1997/.. ../1997 1967-02 2009-01-31...