Here shows the tops of the RC-1, the inside petticoat of the NN and a comparison of the R-3 beside the NN. If you hold the R-3 up to the NN the tops and wire groove are almost the same. It would have been nothing for them to change a mold and make the other cut in the top. I don't have a R-1 to compare with but hope to find one in the future. The R-3 is essentially a redesigned R-1.