Very interesting question, Max. My guess is that in just about all cases, the answers will be almost exclusively 19th Century Ballplayers & Negro Leaguers. While this info would be quite accurate in general from
www.baseball-reference.com like you stated, I believe that 19th Century info would be somewhat sketchy although I do have a good source of info for Negro Leaguers. Also, Umpires and Managers would likely have a sizeable gap as well.