In the past, the air-conditioned bus routes were numbered as 200's (Kowloon and New Territories) and 500's (Hong Kong Island). However, this identification became void after they phased out all the non-aircon buses; and since then bus routes has been playing around with the old numbers.
At one time, there were two "N11" bus routes in Tung Chung, namely, Airport overnight route N11 and Lantau Island overnight route N11. The latter is no longer in service.
The "A" for MTR Buses stands for auxiliary routes, not airport routes.
The numbering systems of public light bus (green minibuses) are classified into Hong Kong Island public light bus routes, Kowloon public light bus routes and New Territories public light bus routes. There are no public light bus in Airport or on Lantau Island. Their route numbering systems are independent too. However, for cross harbour public light bus routes, the route numbers from Hong Kong Island or New Territories are used instead.
Residential bus routes are the routes which are requested to operate by the residents or estates community. At the past, the route numbers are with a suffix "R". The first residential bus route was route 88R from City One Shatin to Kowloon Tong (MTR) (it was then renumbered 62R). From c. 2003, the route numbers have been changed as prefix "HR", "KR", and "NR". They stand for Hong Kong Island residential bus routes, Kowloon residential bus routes and New Territories residential bus routes respectively. There is no residential bus services on Lantau Island (except Discovery Bay) and the Airport.