Sierra Leone has 3 provinces and a western Area. (http://mic.gov.sl/dotnetnuke/AboutSL/Provinces). In the database, I find 4 ADM1. That seems "North West Province" (geonameid 11919533) is wrong.
Are you sure the page is up to date? The north west province is said to have been created in 2017.
Do you have any other information about the new province?