Hi Darren,
The R500 didn't actually supersede the R200, the R300 did: if anything the 500 superseded the RT8, maintaining the choice of two models comprising the Roberts range. A far cry from today's situation!
For my sins (which would definitely be off topic
) over at
http://groups.yahoo.com/group/robertsradiogroup/ I've been keeping a database of Roberts serial numbers from all periods. Numbers of sets currently on file there for the early transistor models are:
RT1 (1958) 63
R200 (1960) 135
RT7 (1960) 9
RT8 (1962) 15
R500 (1963) 23
R300 (1964) 48
R404 (1965) 16
R700 (1966) 16
R303 (1967) 17
RIC1 (1968) 41.
The large number of R200s is pretty well accounted for by the model having had four years as Roberts' standard transistor set: the RT1 just had two years, the R300 three but perhaps its dated style was starting to tell against it. None of the models are rare exactly, but the general pattern is that the line of basic models (RT1 - R200 - R300 - R303 - RIC1) sold well, while the larger RT7/RT8/R404 and the R500 with short wave, which were offered alongside the basic sets, weren't as popular. There aren't so many R303s around simply because the set only enjoyed about a year in production before its replacement by the RIC1.
Regards,
Paul