Single Decker models after the war were numbered S6, then S8 through S23, Double Decker models D1 through D10. The D10 was, in some opinions, the pinnacle of BMMO bus design – a double decker with front entrance/rear exit and an underfloor engine, but only two were produced. AD2, GD6 and LD8 were exceptions to the normal designation system – these codes referred to batches of respectively AEC, Guy and Leyland vehicles acquired when the manufacturing operation could not meet the heavy demand. Individual buses were numbered from (around) 2000 to 5900 – registrations (usually) incorporated the last three numbers of the serial, and a letter prefix of three letters ending in "HA" ( a Smethwick origin registration mark). This relationship did not apply to the limited number of buses gained as a result of acquisition of other operators.