The "OFC Major" came from Dyer's Compendium. I don't really know what it means but guess the F might have something to do with Field as in Field and Staff. Boswell was a captain (no OFC) for a year before he was promoted to major. He resigned as major a year and 3 months later. I see OFC sgt majors, OFC assistant surgeons, OFC Lieutenant Colonels, an OFC Adjutant, an OFC Chaplain, etc. Perhaps someone else knows.