Lights Out - S2-E20
Revealing mistake: When Peter is on stage at his school for the talent show, Cindy gets into the disappearing lady booth and Peter closes the curtain. He says the magic words, yanks open the curtain and Cindy has disappeared. Look at the top left side of the booth and you can see where the stage curtain is piled up on top of the booth. There is just enough room for Susan Olsen to get out of the booth and then get back in.
Lights Out - S2-E20
Plot hole: When Alice brings Cindy to the auditorium to help Peter in his magic act, her cape is already there backstage. She was not going to be the assistant until Jan got hurt. (00:22:10)
Answer: Much trivia has been written about "The Brady Bunch, " including the various interrelationships and dynamics among the members of the cast. For example, much has been written about why Robert Reed's Mike Brady did not appear in a couple of episodes, including the series finale, due to rancorous creative and artistic differences with series creator, Sherwood Schwartz. However, in contrast, I have never run across any reasons given why a particular child did not appear in specific episodes - only that the episodes were missed. This suggests the causes were likely unexceptional, such as illness, injuries, vacations, or real-life family obligations.
Michael Albert
Although those options ARE possible reasons, it just seems a bit ironic that this happened all in Season 2 ONLY and within a short amount of nearly consecutive episodes. Never happened during the other 5 years of the show at all.