RO633's, by virtue of being commercial models, and not official military issue, there were any number of variations, the 633 being a "transitional" model produced while production was being converted from A1 to A2, and more or less used whatever remained in stock, to include A1 lowers and vinyl acetate stocks, transferring over to A2 lowers and fiberlite stocks when the stock had diminished.
~Augee