Shitty Ask Lemmy

"The real McCoy" is not a reference to Elijah McCoy's oiler but predates Elijah's invention and seems to come from Scotland originally. The term has been misapplied to many McCoy's over the centuries.

Elijah McCoy was an inventor who was originally born in Canada to parents who had fled there to escape slavery in Kentucky. They eventually moved to Michigan where Elijah would go on to invent not just an improved oiler mechanism for machinery but also stuff like a folding ironing board and a lawn sprinkler. Despite an interesting and successful life the saying "the real McCoy" was never really a thing. It seems to have been applied retroactively around the 1960's.