The known statistics from seven Black baseball leagues, recognized as "major leagues" by MLB in December 2020, have been incorporated into Baseball-Reference. Research on these leagues is on-going.
While Baseball-Reference has no box scores (yet), Retrosheet does – for 505 Negro League games (209 of which have play-by-play). Those box scores include 35 All-Star games (play-by-play for 28), 210 Negro League playoff games (play-by-play for 91), and 249 interracial games played between 1925-1948 (play-by-play for 79).
The seven new major leagues:
Negro National League I (1920-1931)
Eastern Colored League (1923-1928)
American Negro League (1929)
East-West League (1932)
Negro Southern League (1932)
Negro National League II (1933-1948)
Negro American League (1937-1948)Baseball-Reference (my emphasis):
The Negro Leagues data is not complete.