How we know they’re different people:
Mike Stanton #1 pitched in 277 Major League games, 274 of them in relief, for Houston, Cleveland, Seattle and the Chicago White Sox between 1975 and 1985. He never appeared in a postseason game.
Mike Stanton #2 pitched in 1178 Major League games, 1177 of them in relief, for nine teams between 1989 and 2007, including a total of 53 postseason games and six different World Series.
Mike Stanton #3 got so tired of all the confusion of being a baseball player named Mike Stanton that he changed his name to Giancarlo Stanton prior to the 2012 season. When he made the announcement, he was reportedly quoted as having said “I ain’t no stinkin’ relief pitcher like those other clowns,” but this is unconfirmed.
How we’re not sure they’re different people because we’ve never seen them in the same room together:
Mike Stanton #1 started his career in 1975, but didn’t appear in the bigs again until 1980. He then retired in 1985, and Mike Stanton #2 started his career in 1989. Maybe Mike Stanton #1 just took another break before his second comeback. Think about it. As for Mike Stanton #3, well, he was born that same year, in 1989. Coincidence? Come on.