More likley to be R.A.O.C., I think. The "NC" code was in use for spare parts under the VAOS system and they were responsible for supplying vehicles, parts and literature.

The RAF codes appeared after The Ministry of Supply took over joint purchasing for the War Office and The Air Ministry. They presumably insisted on shared publications.

Thanks Rik & Rob, that explains why I've never seen any later maintenance manuals above 101/NC.3.A. + riders handbooks above 100/NC.3.A.