Coolness! There have been a few Kid Commando stories in the last five years or so. I remember one for the 70th Anniversary specials.
Robinson is clearly adding to the WWII Invaders history with these flashbacks. Isn't it possible that Union Jack and Spitfire would have rejoined, had they been asked? Spitfire is specifically on the team because her powers make the tsunami possible.
I mostly think of Whizzer and Miss America on the homefront side of things, with Liberty Legion, myself, though I know they also were with the Invaders at various times.