Thanks for posting that. That is very interesting. Are there any set changes in the NOM, or only in Fred's house? What about in the opening and closing credits? I wonder if when Episode 21 was re-shot, if they re-shot the entire episode, or just the NOM.
Another curiosity is Episode 10. Barbara Russell is listed on the production slate and in the end credits, but she does not appear. However, Betty Aberlin does appear in the episode, but does not appear in the production slate, nor does she appear in the end credits. That leads me to think that the NOM was probably re-shot in that episode.
A possible hint as to when NOM segments were shot could be Betty's hair. I seem to remember it being very short in the early 1968 episodes, but very long in the 1969 and 1970 episodes. The RFK assasination special was obviously shot in early June 1968, and I seem to remember her hair still being short then. That means she probably grew her hair during the summer of 1968. If she has longer hair in a 1968 episode, it means the NOM was probably shot later during the summer of 1968, regardless of the date on the production slate (which may have been only for the real neighborhood parts).
Another strange thing I noticed: until 1971 (when many holidays were moved to Mondays), Washington's Birthday was Feb. 22, Memorial Day was May 30, and Columbus Day was Oct. 12. Strangely, episodes were shot on all 3 of those dates! I'm not surprised about Washington's Birthday or Columbus Day, since those are minor holidays. But it seems very surprising that Fred would have shot an episode on Memorial Day. I wonder if maybe the May 30 version of Memorial Day was a more minor holiday than today's Monday holiday that kicks off the summer. Or I wonder if maybe Pennsylvania moved Memorial Day to a Monday before it was done nationally (unlikely). Thanksgiving would have fallen on Nov. 23 in 1967, and I'm surprised that they shot an episode on the Friday after Thanksgiving, which nowadays is a de facto holiday.
It also seems that there was only a 1 week break in between the old set and the new set, with the old set used in the episodes shot on 11/1/67 and the new set in the episodes shot on 11/8/67. I had pictured there being a much longer break.
Another question for Tim: do you have production dates for the 1969 and later episodes?