Continuity mistake: In the kitchen when Jan announces that she took up tap dancing, Mike's first button goes from buttoned to unbuttoned a few times during the scene. (00:06:00)
Continuity mistake: The kids walk into the kitchen complaining about the noise from Jan's tap dancing. Peter reaches up and grabs his paper sack lunch and then in the next shot he says "talk about noise pollution" while grabbing his lunch for a second time. (00:09:07)
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.