A fella in the number plate trade told me a lot of people bought up cheap R20 plates when it was rumoured R20 in the hope of making money when it was officially announced.....that would have been marketing crazy to have it a lesser number than the R32, hence they went with just the R.
R20 plates not worth as much now I am afraid. As above though, try the R forum and also maybe worth on R32OC.