I'm glad someone else once asked this same question that I had. The answer is, there's no source for the name Calvin here. I looked at other sites such as Geni and FamilySearch. Their only source goes back to a record regarding an unrelated John Calvin White who was born in 1947! In other words, someone mixed up a John Calvin White from the 1900s with our John White from the 1700s (my 4th great grandfather) and incorrectly gave the latter a middle name that he apparently didn't have.