Why is there a 14th Noah?
Unanswered in the manga as of now, but it is entirely possible that there are 14 Noah and the Earl only mentions 13 (including himself) because the 14th apparently dislikes the Earl, as he wants to dethrone him and take his place. Chapter 218 hints that a "Mana D. Campbell" may be responsible for the existence of the 14th, although i can´t really call the Earl in his current state of mind a reliable source.