Season 5
Episode(s) were Wally's date had to drive them to the dance and the other episode where Beaver and Wally go to a dance and the go through the reception line and Frank was there, but not Eddie.

I think on a past thread there were comments about his absence on some season 5 episodes (episodes like you mentioned that he would obviously be part of)...one theory was that he had other parts (like maybe a movie), or was sick. He was also gone for much or all of the last part of season 2.

Maybe Eddie was directing the episode.

Or in jail.

I agree it is strange how Eddie is missing especially when Evelyn Boothby drives Wally to the dance but is there in Wally's Accident when he smashes headlight.