When I was watching The Beverly Hillbillies last night on TV Land, during the episode I thought I heard Jed calling Elly by her real name, "Donna". Could it be that that got through without anyone catching it? Or is it just my imagination? It was the episode where Granny makes Shorty do all the chores and at the end Shorty leaves to go back to the hills.

It's quite possible. I remember an episode of Sanford & Son where Lamont calls Janet by her real name (Marlene). Also I've heard that there is an epsiode of the Brady Bunch where Greg calls Jan by her real name (Eve).