Variety's article has a full list of episodes which have the disclaimer:
The disclaimer has been added to a total of 18 episodes throughout the show’s five seasons, including those guest hosted by Jim Nabors, Joel Grey, Steve Martin, Peter Sellers, Cleo Laine, James Coco, Spike Milligan, Crystal Gayle, Kenny Rogers, Beverly Sills, Jonathan Winters, Alan Arkin, James Coburn, Joan Baez, Johnny Cash, Debbie Harry, Wally Boag and Marty Feldman. The label has been added to each episode for a different reason; but for example, during Cash’s episode, he sings in front of a confederate flag. The disclaimer appears at the beginning of these episodes for 12 seconds.