C.E. Evans wrote:
IIRC, TOS actually gained more viewers after it was cancelled. Once in second-run syndication, millions more were able to see the show because it was scheduled outside of primetime (depending on where you were, it was either on weekend afternoons or late nights on your local station).
I see this claim a lot and often wonder if it is true. It certainly is true that the original series was a great success in syndication, but did it really have more viewers in re-runs than first-run? I don't doubt that, over time, more people saw the series after it was cancelled than had watched it on NBC, but was there really an audience at any one time that was bigger than the one delivered by a major network during the three network era?
TOS wasn't just syndicated in the US but in sixty other countries (where it was translated into other languages for some). It was really after the show's cancellation that it got its biggest following. It's impossible to say if it had a bigger audience at any one time
after leaving NBC because it often aired at many different days and times in syndication, but definitely many more people saw there due to its greater presence in both US and international TV markets and its length of time there.