How did John McGraw prove the common claim that baseball's segregation was not official but just something every team went along with to be a lie as noted in the biography, Oscar Charleston: Was Cobb “The White Charleston”?

Famed player and manager John McGraw, throughout most of his career, tried to sneak African-Americans on his teams, the most infamous instance being a case in which he signed a second baseman and pretended he was an Indian. Charles Comiskey of the Chicago American League club figured out that the player was black and told league headquarters, which removed the player from McGraw's team. This puts the lie to a common claim that baseball's segregation was not official but just something every team went along with. If that were the case, McGraw would have had his second baseman for a long career. It has been said that among McGraw's effects after his death was a list of the African- American ballplayers he had wanted to sign during his career.