The Finns also used Fokker DXXI’s, and the NEI forces also used Brewster Buffalos… which means that the Finns and the NEI forces were both using both Buffalos and DXXI’s for opposite sides in the war: boy they sure knew how to pick 'em, those Finns!
But anyway…
…so either the Buffalo or the Fokker DXXI could be made in the white version of the Dutch/Neutral set and serve for Finnland without it being in this set. If you also run the neutrals set in yellow and green, (which would be cool, as the Dutch infantry used Romanian helmets, or rather the other way around) then you could use any of the Dutch aircraft or ships for Axis neutrals if a situation occurs where it makes sense…
Which makes me think, you should consider adding the Fokker G I to the Dutch/ Neutral set for a tac bomber
If you do those two things (1. add Romanian yellow & Bulgarian green to the Dutch/ Neutral color run & 2. add Tac Bomber to Dutch/ Neutral set) then the Axis minors have anything air or naval that they might need covered by either the Dutch or the German air/naval set, and the Axis minors set can safely stick with land units. (This is, of course assuming that the Axis minors will never be able to afford something as expensive as a heavy bomber, battleship or aircraft carrier… but I’d say that’s a pretty solid assumption… :-D)