 In addition to the rules above, Keighley- and York-West Yorkshire bus fleet numbers were prefixed with K or Y as appropriate so, for example, Keighley-West Yorkshire Bristol K6B reg no.GWX 125 was given a fleet number of "KDB30".Over the years, several exceptions to these rules evolved, including DX (Double deck eXperimental), used to denote Bristol Lodekka buses, SUG/EUG/CUG (Single-decker/Express/Coach Underfloor-engined Gardner), SMA/SMG (Single-decker Mid-engined Albion/Gardner), SRG (Single-decker Rear-engined Gardner), VR (Vertical Rear-engined – Bristol VR type)

In October 1971 the fleet was again renumbered and the class identification letters disappeared as the fleet identifiers once again reverted to purely numerical system.