Difficult to judge the popularity of any of the IRM A class since a set number was not necessarily made, unless you have access to that close to the chest information? Popularity of the A46 liveried one could be related to the prevalence and longevity of the prototypical livery, anticipated demand, general appeal of the particular livery, batch sizes of other A class models, etc etc
Given that the dark green livery was the official type for a decade, versus about 8 years for the lighter green, I presume the relative lack of light green in traffic is related to displacement by the substantial bogie coach building program of the early 50s, and some delay in repainting the dark green into light green particularly of they were being cascaded to secondary routes? Its a shame that we don't have an Irish rtr steam engine to pull these, other that a OOworks J15 I mean