Hmmm . . . that would be interesting to look into. The Eagle Squadrons only had 244 US pilots. But around 6,700 were accepted by the committee to become RAF pilots. You're quite right. It would be good to learn where they ended up. I've read somewhere that it the RAF approach to pilot training was this: If one could fly an airplane, one could fly all airplanes.
If so, those US pilots could've ended somewhere else in the RAF.