anyway, for a short time the Spitfire IXs with Merlin 61&63 were unofficialy called Mk.IXA and the ones with Merlin 66 Mk.IXB.
totaly indepentend from their armament - all had 2x20mm and 4x.303cal :D , at this time !

Good post Ospery, obviously the official suffix and prefix system was made up as early as 1941.

Yes it seems by good collaboration too.

Frankyboy, what's your source? The only reference I could find was MkI's which were upgraded to MkV's which temporarily carried this naming convention (VA) because the wings were not replaced on the very first. Only about 120 (memory from last nights reading) of the Mk VA were produced.
This wasn't uncommon to fighter production, as new developments came in the factories would use up old stock of sections which is why you sometimes see strange configurations in airframes on particular Mks. It makes sense, resources were precious and the Mk IX was a MkV which was a MkI. The development and testing of these combinations was constant and they kept on spewing out the hybrids.

Alfred Price Osprey Aircraft of the Aces volume 5 "Late Mark Spitfire Aces 1942-45"
page 14

sure thing, i'd like that.