Re: 'All Our Yesterdays' theory
One of the problems with third season episodes was there often wasn't anyone around riding herd on the scripts to make sure they were consistent with earlier stories. The job often fell on the actors themselves (Nimoy in particular regarding Spock). Even Shatner argued with the director of "Turnabout Intruder" when he wanted Kirk to exit through a door in the briefing room that was never established as being there.
Dr. Howard, Dr. Fine, Dr. Howard: For duty and humanity! --Men in Black (1934)