Historically, these plates were used on buses, taxis, livery vehicles and rental cars.
Starting in the 1970's, when unique livety-type plates were issued, OMNIBUS plates were only used on buses and taxis.
1960 BASEOWA-100 - OWZ-999
The initial issue (OWA through OWZ) has tab slots, but tabs were not used - the plates were validated with stickers.
1969 BASEOXA-100 - OXZ-999
Some of the early OX series plates were reflectorized - from at least OXG to OXM.
The OXX series was *not* reflectorized.
1979 BASEOYA-100 - OZZ-999(?)
The highest number known on the blue base is OZR-485.