BB,
I now see your point: when Peter C. Smith sets out, at length and in great detail, the history of EZ999, and then says that "the markings EZ999 now carries are fictitious", he is referring, not to the "EZ999" itself, but only to the squadron letters and nose art on the aircraft.
But it is not uncommon for display aircraft (as in this case) to bear squadron markings, etc "to which they are not entitled", just to make the display a bit more lifelike. Sometimes a row of bombs or swastikas, or 2nd TAF stripes is added for effect. This is well known and Smith hardly needed to draw attention to it.
Be this as it may, it seems that the difference between our opinions is based on this misunderstanding and can now be laid to rest.
I am not yet convinced, but await the physical evidence (AoI and front gun mountings) to settle the matter (and where did that weird cockpit panel come from ? - it is unlike any Mk. I-III, which all had the same panel, no reflector sight, just a simple ring 'n bead)
All the best, Danny.