Aqui estão algumas citações do artigo da Wikipédia sobre o Jornada de Star Trek (Ousado meu):
People who worked with Roddenberry remember that he used to handle canon not on a series-by-series basis nor an episode-by-episode basis, but point by point. If he changed his mind on something, or if a fact in one episode contradicted what he considered to be a more important fact in another episode, he had no problem declaring that specific point non-canon.
See, people can easily catch us, and say "well, wait a minute, in 'Balance of Terror', they knew that the Romulans had a cloaking device, and then in 'The Enterprise Incident', they don't know anything about cloaking devices, but they're gonna steal this one because it's obviously just been developed, so how the hell do you explain that?" We can't. There are some things we just can't explain, especially when it comes from the third season. So, yes, third season is canon up to the point of contradiction, or where it's just so bad... you know, we kind of cringe when people ask us, "well, what happened in 'Plato's Stepchildren', and 'And the Children Shall Lead', and 'Spock's Brain', and so on — it's like, please, he wasn't even producing it at that point. But, generally, [canon is] the original series, not really the animated, the first movie to a certain extent, the rest of the films in certain aspects but not in all... I know that it's very difficult to understand. It literally is point by point. I sometimes do not know how he's going to answer a question when I go into his office, I really do not always know, and — and I know it better probably than anybody, what it is that Gene likes and doesn't like.[3]— Richard Arnold, 1991
Another thing that makes canon a little confusing. Gene R. himself had a habit of decanonizing things. He didn't like the way the animated series turned out, so he proclaimed that it was not canon. He also didn't like a lot of the movies. So he didn't much consider them canon either. And – okay, I'm really going to scare you with this one – after he got TNG going, he... well... he sort of decided that some of The Original Series wasn't canon either. I had a discussion with him once, where I cited a couple things that were very clearly canon in The Original Series, and he told me he didn't think that way anymore, and that he now thought of TNG as canon wherever there was conflict between the two. He admitted it was revisionist thinking, but so be it.[4]— Paula Block, 2005
CanonWars.com tem estas mesmas duas citações, bem como um monte de mais informações sobre todas as séries posteriores e as filmes.