So, should the section of "Airport Way, Gatwick" between exits 9A & 9 be removed from that file and added as a separate M23 file?
No. It's not signed as M23 away from the motorway. The DLS signs don't count - they have it as sliproads as they use 'L' and 'M' (the standard 4 ramps are J, K,
L and M). The included motorway spurs have it explicitly on the DLS that it's a spur.