Introduced in Blood and Chrome. Very similar to the Mk II so I didn't spot it at first. The fuselage seems more bulky, the cockpit canopy seems more rounded and the wings slightly larger.
Didn't think we'd see anything else but I thought this was a nice easter egg considering it'll probably be the last BSG we'll see for a while.
Does raise the question why Mk IIs are still being used in Razor...
It does seem to be a bit of a continuity error with both Razor and
the pilot, since Adama was supposed to have flown a Mk. II
durring the war...but in the pilot we saw the saw a Mk. II that
Adama flew durring the war...yet in Razor was saw him ditch
his viper on that planet at the end of the war...bailing out...so
it seems like his viper was destroyed...