Despite appearing in several scenes (with dialogue) as "Cpl. Cuccinelli," co-star Tommy Leonetti does not appear in this episode's closing credits.
Per the title, a "Dear John" letter is a message to a soldier or one far away from one's wife or girlfriend that they are breaking up.
When Carter and Gomer are talking in Cater's office, the shadow of a book mic is visible on the office door.