The die cut perfs are blunt on SG 823a, they measure 9.5x9 and there is a narrow tooth protruding at each corner. The die cut perfs are pointed on SG 823, they measure 11.4 and these stamps do not have the narrow protruding teeth in the corners. Stamp Number lists a third perforation variation (perf 11) which is not in the other catalogues and perhaps do not exist.
