I guess it's an enigma for now. Based on your information, my suspicion is that "John" was probably an older man whose marriage to Ellen was presumably his second or third. Given that two of the three Devill lines were based in Hints (near Tamworth) a century earlier, it seems feasible to me that John was descended from one of these. A "John Devell" is also recorded in Tean (spelt "Tene") near Uttoxeter circa 1450, while another "Deyville" is listed as a priest in Alton/Alverton in the 14th century, indicating that the "Devells" were/are probably an old (possibly Norman?) family with several distantly-related branches spread across the Midlands. Do you have any details on the "older" John's birthdate and parents?