I’ve never heard of that, but it would undoubtedly be because of story linking material changes, not for any kid confusion, which wouldn’t have been viable in the 70s, just like it wasn’t for the links in the Warners cartoon compilations that have wildly different character designs often in the same scene!
As for the "canon"...in truth there’s never really been one (and, actually, probably shouldn’t be one)!
A "canon" in the sense of the word, suggests a series that has some connection, in which events and occurrences make up the "history" for future events and reference. In this instance, there is nothing "canon" about Disney's animated features, other than this word being inaccurately applied to a list of Disney's animated films.
Even then, there was never such a list, since until at least when television came along, every film that was released by Walt Disney Productions was A Walt Disney Production and went on that list, usually under their production banner code (Mickey Mouse, Silly Symphony, Donald Duck, etc), with featurettes labelled as Specials (most of the post-Symphonies) and Features being, well, you know, feature films...be they animated, combination or live-action.
It’s really when TV came along that outside sources began making up books and such and compiling lists of Disney animation properties, and this is where the first listings of properties that featured Disney animation came from. The compilation features such as Academy Award Revue and Mickey's Birthday, were not included, but practically everything else that had a Disney animation sequence in it was, including Air Power, Reluctant Dragon, Song/South, Dear To My Heart, the Package Features, Poppins, Broomsticks and Dragon. When I wrote to Disney's UK office in around 1981/2/3, they sent me the "official list" on Disney paper, so I know this was "fact" back then.
At one point, the Package Features were NOT included in some lists (again, mostly outside sources) because they were not full features and considered compilations. By 1985, Katzenberg came in and revised the entire list to exclude the combinations and just focus on full-feature animated films, making Cauldron the 25th, to give it some prestige-sounding number for marketing purposes. That became the list from then on, though it’s in recent times and the rise of the internet that the word "canon" has been applied, however inappropriately.
(Dinosaur is included because it was produced by WDFA.)
What’s the story on "Walt's Epcot film"?