After having watched the I Love Lucy x Adventures of Superman episode, it feels to me that the Superman who appears is actually Superman, not George Reeves. Yes, that would mean that Adventures of Superman also exists as an in-universe show, but that's not hard to believe. The few winks that could be taken as "it's an actor" can be easily explained away, like Superman has to take a flight, or that one character met Superman in Hollywood. The fact that he appears to have superhuman strength confirms it for me. But yeah, including I Love Lucy and everything connected is just impossible (as I actually ended up with another version of Superman in here before stopping). It's a bummer, but yeah, if sitcoms enter the mix, we can't count every single crossover