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barrysloateThere are so many books published with the title "Who's Who" that it can get confusing. The most popular is the 1933 Speed Johnson volume.
But there was also a yearly series published by John Carmichael titled "Who's Who in Major League Baseball." That annual lasted from 1938 to 1955. They are found frequently and I am guessing that is the one you reference.
And there is a current "Who's Who" that is up to its 94th edition this year. It's the same idea as the others, offering career statistics for every active major league player.