Regardless, that's. the. point. D&D and AD&D (i.e. "different games") was nonsensical except as an attempt at dodging royalty payments. "Editions" as AD&D and AD&D 2nd Edition used them deviates from the publishing standard (although probably not dictionary) meaning of the term. The different iterations of the game most closely resemble differing versions of the same product line, by which I mean they can be ostensibly 'the same thing,' yet at the same time broadly different* either in outward appearance or underlying mechanics. *or not. Sometimes you just change the thimble and iron for whatever are now included in Monopoly sets.
So, I have to disagree with this.
First, "Advanced D&D" was not cooked up just to avoid royalty payments. That's a common misperception, but the reality is a lot more complicated. TSR had a good faith belief that Arneson was only due royalties on the sales of the original OD&D ruleset- not any additional material. It's more complicated that that, and I suggest reading
Game Wizards (I think I've mentioned this a lot recently) to get the full details, but it's not true that the purpose of AD&D was to dodge royalty payments.
Next, the delineation of lines. The first Basic was not "Basic" was we normally think of it, but
Holmes Basic, which was actually a cleaned up version of OD&D. Inserted into it was a reference to the forthcoming AD&D.
When you view it that way, it makes a lot more sense. AD&D wasn't a "new edition" per se. And Basic certainly wasn't a branching line.
Instead, Basic was the cleaned up OD&D rules. AD&D was also OD&D, except with all the supplements, a bunch of additional previously published material (such as Strategic Review and Dragon articles) as well as some new material, edited and put together. But Holmes Basic was just levels 1-3, and was more of a "starter set" to the
Advanced D&D. Even though Holmes had different rules than AD&D, because ... reasons.
The later Moldvay/Cook B/X and Mentzer BECMI was the result of the litigation, and also looked back to OD&D, albeit with revisions (such as race-as-class). While this was interoperable with AD&D, it was also a different game.
The idea of different "editions" only arose with 2e, which became confusing because, unlike future editions (3e, 4e, 5e), 2e was just AD&D (1e) but edited and changed up a little. But there was nothing that was
fundamentally different about it, which was not true for the later edition changes starting with the WoTC era.
TLDR; trying to understand what is, and isn't, an edition in D&D is an exercise in frustration, other than acknowledging the actual editions and reasoning from there.