A number of points that are in response to many of the comments made.
There is extensive research on the caliber of play in the Negro Leagues, and generally it is assumed that the stars were roughly equivalent to the best in the Majors, while the leagues overall were in the range of AAA (or between AAA and the Majors). This is based on a wide range of factors including barnstorming tours, common opponents etc along with seeing how players who transitioned leagues like Jackie, Campanella,Doby and others did.
Note that there were a number of leagues historically that are considered Major Leagues. Along with the American League and National League, there was also the Union Association, the Players' League and the Federal League. And the range of talent in those leagues varied significantly. Certainly, in some cases, they were no better than AAA, which means that we currently have official leagues that were on par with the Negro Leagues and likely were worse.
The stats that will be included are only from 1920-1948 which was when the leagues were more structured and established, and before integration largely impacted the caliber of the teams and players. And it is only for league games.
There has been extensive research on Negro League games and box scores. There is definitely still uncertainly around stats, but we have uncertainty around stats from the 1800's as well and that never stopped us from including them. We've had adjustments to major stars. An adjustment to Ty Cobb's total (which is now reflected in Baseball-Reference) is in the article below.
https://sabr.org/journal/article/how...tting-average/
Regarding some comments about the push for this; while the average fan, who cares little about the Negro Leagues may not have heard anything about this, there has been a push for some time. I wasn't involved in the push, but think it is a good thing.