Okay, I did some research, and apparently this is a fan myth that's rooted in some degree of truth. Yes, there were two separate production cycles, one with 13 episodes filmed from September 1966 to April 1967 and one with 4 episodes filmed from August 1967 to January 1968. But no, the second cycle was not a second 13-episode season that was cancelled prematurely. http://numbersixwasinnocent.blogspot.com/2009/09/mcgoohan-on-my-mind-number-of-beast-or.html There's no question that it was McGoohan's own choice to make it a limited series. He didn't like the idea of dragging out a concept indefinitely, and even 17 episodes was more than he wanted and the absolute maximum he would agree to. The network absolutely did not "cancel" the series -- McGoohan ended it on his own terms. Not only considered to be, but definitely was. Battlestar Galactica was cancelled, period. Its cast and crew moved on to other projects. But ABC had lost a lot of money on the show and pressured Larson to make a sequel series that would amortize the cost of the sets, props, costumes, and stock footage while being shot in a more inexpensive Earthbound setting. Since most of the original show's creators and stars had gone, G80's production had few people in common with the original. It was definitely a separate series, a sequel rather than a continuation. (Not to mention a soft reboot, because the original was pretty clearly in Earth's future, and the sequel series supposedly set decades later was in Earth's present.) The basis for the confusion is that G80 was folded into BSG's rerun-syndication package and the episode had their title cards changed to read Battlestar Galactica, creating the impression that it was a continuation of the same series. On the other hand: That's definitely a single continuous series. Despite the title, network, and format changes, it was a continuing production with largely the same cast and crew. ABC was hesitant about renewing the show because of its period setting, so CBS swooped in and offered the producers a pickup if they'd move it to a contemporary setting and a more standard '70s adventure format.