As far as the shows spit being the only two-seater Mk9 in the country, I don't believe that is correct. A Mk9 flies into the airfield where I work from time to time, and while Im not SURE its not the same one, the absence of the "invasion markings" in my photos seems to suggest they are two different planes. I believe this one was recovered from North Africa some time after the war for a complete restoration.
Check out this pic of the Mk9 with my own Mk3 Spitfire
Mk9 and Mk3 together!