Yup....hold over from when we had the 737-200 (737 or 73S if part of Delta Express), 737-300G (73G) and the 737-800 (73N) all flying at the same time. The -800 was Next Generation so it got the N code. And then there is the 765 which is really a 767-400. At one point, ATL had a domestic category (764) and an international category (765). Guess they decided to keep the "5" instead of the "4" to keep it confusing. 😁