With birth date range as criteria, the name search does not render results for pages that have birth year data but no birth month data.
When a birth date range is specified in the search query parameters, the Advanced Name Search does not render results for name pages that have birth year data but no birth month data or no birth day data. Take Jace Norman, for example. The year of his birth is recorded in the appropriate and effective data field of the name entry about him, but both the "month" field and the "day" field are empty. For a query like https://www.imdb.com/search/name?roles=tt4648586, a reference to him appears in the collection of results, whereas for a query like https://www.imdb.com/search/name?birth_date=1998-01-01,2002-12-31&roles=tt4648586, there is no reference to him in collection of results, which is quite counterintuitive seeings as how the year 2000 takes place entirely within the time span between the first day of year 1998 and the last day of year 2002. The aforementioned case is just an example case, used to convey an explanation of the overall situation. The problem is that it is impossible to use the Advanced Name Search to search for name pages that logically fall within the specific criteria of birth date ranging, if those pages have anything short of birth date data that includes not only year but also month and day. It would be great if this technical shortcoming could be overcome via the implementation of the necessary software upgrades to the site/interfaces.