I'm not saying he isn't free to change the story, just that there's a ton of evidence he forgot the original story. But no, he doesn't know more about the original manga than a lot of his fans. His interpretation, while I respect it, is just another interpretation. You're pulling his god like authority out of your ass. Sure I get that a lot of people do see the author as ultimate interpretation but it's not really based on anything. If I've learned anything in my literature classes it's that the author's intentions aren't quite as important as how the readers interpret it (see Death of the Author). While you can use context of the author's historical stand point to better understand the manga (such as the Saiyans being the foreigners post WWII), that in itself shouldn't have any bearing as to canceling out what the original story said.
Someone can memorize the manga line by line and defeat AT on remembering the story. Does that mean that AT's misremembered version is better? No, it doesn't, at least to people that don't see it that way. I don't respect the viewpoint that people would prefer the misremembered version over the exact version. My lack of respect for AT has no bearing on the evidence that he's forgotten his story. Not to mention that Super goes through a lot of filters and AT hardly writes all of it (only saving grace).