Likely June or July 1967 dispatch date. My G15CS is less than 200 numbers higher and it was shipped in July.
G15CSR had a handful of differences from the CS - usually a larger, chrome tank, low bars, swept back exhaust (Domiracer style), chrome fenders, rearsets and a reverse cam plate in the transmission with the gear numbers reversed on the brow on the cover. CSRs also had thinner spokes on the rear wheel - no need for the heavy spokes of the CS, as the CSR was intended for road use only.
CSR was a variant of the G15, G12, G11, G9 and even the G2, along with the AJS versions
Matchless came up with the letters around 1950 to differentiate the different models - 'S' stood for Sprung, as in swingarm frame rather than rigid; 'C' stood for Competition, usually with a smaller tank, lighter fenders, different seat, and folding footpegs; 'CS' stood for Competition/Sprung, and 'CSR' stood for Competition/Sprung/Road, but was usually referred to as the 'Coffee Shop Racer'
Equipment varied from year to year, with some of the last ones even shipped with 12" rise bars and a stepped seat - referred to as the 'apehanger' CSR