The fact is, you gotta believe what you want is canon,
Except that's not canon, that's personal continuity.
We have a definition of canon, however much people want to ignore it. All live action films and TV series are canonical as they appeared on screen. Everything else, be it animated, books, comics, RPGs, etc, is not.
What you want to have as your personal view of the "universe" is entirely up to you. But it has no more baring on the canon of Trek than saying you don't accept the book of Jonah would have on the books of the accepted canonical Bible.
Okay, so the episode of the cartoon when Spock goes back and visits himself is as child is, but Robert April is not. Hmm. I'm not saying you're right or wrong, I'm just saying why believe one and not the other.
As far as I'm aware, neither of them are. Yesteryear is a popular episode among fans and so many would like to believe that it happened, and so they count it in their personal continuity, but it was never officially recognised as canon after TAS was thrown out of continuity. I'm unaware of Paramount's policy on canon having changed in recent years, or if CBS has a different take on the subject.
I happen to think that it's all a bit silly. I believe that Gene Roddenberry retroactively "decanonised" TAS because he was unhappy with the way it had turned out. Various writers have included subtle references to it in live-action episodes, such as the name of Kor's ship, and it was the first place to establish Kirk's middle name as Tiberius. So, information contained within the animated episodes is not without merit, but unless CBS indicates their position on the subject we just don't know.
I don't see that happening any time soon, though. It's just one of those things that only we fans care enough about to get worked up over.