Re: the TTTT set change -- comparing the matchgame.org TTTT listings with Marshall Aakers' site lets us pin down some milestones in the series' run.
Buzzr's episode number for the Redenbacher and dog food episodes are the same as those on Marshall's site, so his index must have the seasons correctly divided:
http://www.ttttontheweb.comMatchgame.org does have accurate panel listings (along with GSN airdates and even tape dates when the series was rerun in "WinTV" format), but the first 13 weeks of S3 are misfiled at the end of S2, throwing the season divisions off:
https://web.archive.org/web/20030401082939/http://www.matchgame.org:80/episodeguides/tttt/It would seem that the set changed from its psychedelic hues to the blue/pink/gold appearance starting in week 5 of S3, or week 83 of the sydicated run. (I'd guess that the same set was used from 1969 until early 1973, just with a new paint job midway through, and there were some touch-ups even during the psychedelic weeks.)
The blue/white set with the block-letter logo was introduced with the taping session of 1-23-1973, corresponding to week 31 of S4 (week 148 of the syndicated run).
No idea when the series moved from the Ed Sullivan Theatre to 6A.