Understood and fully appreciated Robert - which is why for the sake of greater realism, it's desirable to use the capacity which does exist to feature a representative appearance, rather than an exceptional (or possibly inaccurate) one.
For example, MJF Bowyer's 'Fighting Colours' features a multi-view drawing of Hurricane I L1768 GG-K after delivery to 151 Squadron in January 1939 (before the ID letters changed at the outbreak of war) and this DOES feature SMALL B Type blue/red roundels on the upper wings (and fuselage sides for that matter). And the same book even has a photo showing L1934 OP-D of 3 Squadron with one such small roundel on the port upper wing and none at all on the starboard, which the author says he saw 'on quite a number of fighters including Spitfires'. And there's a pic of 611 Squadron's Spits at Drem in April 1940 in the Osprey Spit I/II aces book with what looks like exactly the same small upper wing roundels as featured on the WotR Spitfire. But during the BoB, most (if not all) squadron service Spitfires had the regulation, larger Type B roundel on their upper wings, so if there has to be one type of roundel in that position on the WoTR Spit, the larger one is objectively the more realistic choice. Just like if you HAD to choose a single RAF fighter undersurface colour for the BoB, easily the most representative choice would be Sky/duck egg green, not the earlier black/white or aluminium.
Not that bigger or smaller upper wing roundels would have helped with the first engagement featured here:
As for the gas warning patch, without it seems to be the most common for the period, and a vet quoted in 'Scramble! - a narrative history...' mentions seeing them in many places, but not actually on their aircraft.