Louisville, Ky.

American Pharoah became horse racing’s 12th Triple Crown and went into the history books with a misspelled name. That won’t be a problem this year, as all 20 horses entered in Saturday’s 142nd Kentucky Derby pass the spell check. The harder test for the owners of each of the horses may have been getting through the naming rules established by the Jockey Club, the organization that registers thoroughbred horses. Names must be 18 characters or less and must meet a long list of criteria—nothing vulgar, commercial...