The AD&D previews in Holmes Basic were added after the fact by Gary for marketing purposes. This is a fairly well-known fact. OD&D + the Supplements + some scattered Strategic Review and The Dragon material begat AD&D. (And as we know from interviews with Tim Kask, the creation of AD&D was pretty much him and Gary cutting up and reorganizing/recompiling/rewriting what was there. I don't think Holmes Basic had much to do with that. Which makes sense, given that Dr. Holmes wrote the Basic Set on his own, and it and the first AD&D hardcover both came out in 1977.)
There is a clear through-line, meanwhile, from OD&D to Holmes to B/X to BECMI to Classic. There is a reason that B/X clerics are still getting both 3rd and 4th level spells at the same experience level (just like in OD&D), or why BECMI straight up calls itself "the original DUNGEONS & DRAGONS game!" in its own text.
1974 White Box > 1977 Blue Box > 1981 Pink Box > 1983 Red Box > 1991 Black Box is the D&D lineage.
0e (White Box + Supplements) > 1e > 2e > 3e > 4e > 5e is the Advanced D&D lineage.
Magic-users in Greyhawk and 1e got 11d4 from hit dice. Illusionists got 10d4, and in 2nd edition so did all wizards.
While I appreciate some of the things you wrote which are correct, your conclusions are largely incorrect.
The two errors that I see (and that drive me crazy) are these:
1. You continue the incorrect assertion that Holmes Basic is of the line of Moldvay Basic. That's an absolute no.
2. You disregard that certain exogenous event that is related to all of this (aka, Arneson and legal issues).
So, to go into the full details which I normally avoid for purposes of brevity-
OD&D (aka the White Box and its supplements, which also includes additional material necessary for understanding it, such as Chainmail and material from the Dragon and Strategic Review) is the
ur-D&D
. Of course, OD&D, today, is nearly unplayable without some understanding or grounding in the practice of playing then. It is, quite literally, a hobbyist's game. This is all from '74 to '76.
TSR hires Dr. Holmes in 1977 to create a unified "Basic" D&D that incorporates aspects of Supplements 1 & 2. It also included "OD&D" modules (B1, then B2- bonus fun trivia, these eventually migrated to the later Moldvay/Mentzer platform, but you can still find some OD&D goodness in them). At the same time, TSR was releasing "Classic" D&D (the White Box) while announcing "Advanced" D&D (aka 1e, aka the Gygax edition).
Whew. 1977 was a big year! So, the White (Classic), the Blue (Basic) and the Intangible (announcement of Advanced- remember, when you say that AD&D was "released" the same year, it wasn't. The monster manual came out that year. The PHB came out summer of '78, and the DMG was late spring '79).
Why? What was TSR doing? Well, very simply - they were screwing Arneson out of royalties. Advanced D&D was a "Gygax D&D" and therefore not part of the D&D line that was going to allow Arneson to get his royalties.
But to be clear what Holmes Basic was- it was Dr. Holmes making an accessible, readable, and playable version of OD&D. I don't want to minimize his contributions as a mere editor; there are distinctions between Holmes Basic and OD&D (LBB+ Greyhawk), everything from certain demi-humans having minimum ability score requirements to magic missiles requiring a roll to hit to dexterity for initiative. In addition, there is the small matter that there was clearly coordination between Gygax and Holmes as Gygax added material to the Holmes original manuscript prior to publication (such as flaming oil)- therefore, it would be incorrect to say that there was no coordination between the Holmes edition and the upcoming Advanced D&D by Gygax. In fact, AFAIK, there is a lively debate as to the possibility that Holmes was hired to write an introduction to OD&D and Gygax "edited" portions of it to make it more of an introduction to AD&D, but that is neither here nor there.
Which leads us to the lawsuit. "Advanced D&D" is obviously a continuation of OD&D and within the same lineage as Holmes- it's just more. A lot more. And renamed and slightly modified in order to not pay Arneson.
(Side note- just to show you how absurd all of this was, just prior to Arneson filing, TSR had announced that there would be an "Expert" set from the Holmes Basic rules, despite the rules themselves saying they lead to Advanced D&D, solely to avoid paying royalties, because Advanced was incompatible with OD&D ... for reasons, or something?)
So you have a distinct lineage going on. You have:
OD&D. Holmes Basic. AD&D. They are all part of the same root.
Then, in 1981, you have a settlement of the Arneson lawsuit. At that time, you have the introduction of .... Dungeons & Dragons. Aka, Moldvay/Cook. Aka, "Basic" (or "B/X"). (And this is without going into the whole, "Arneson gets paid for D&D, but not AD&D, except for certain things etc.").
Now, B/X is
compatible with AD&D. And with OD&D. And with Holmes Basic. But they are different in terms of lineages. The easiest distinction to make, of course, is "race as class." Essentially, however, the "Basic" line is a fork in the road. While it is compatible with the "Advanced" line, it is a separate path completely- one that has more a little to do with that certain lawsuit. While Moldvay took the very basic LBB as a baseline, however, he ignored the OD&D supplements. Personally, I think Moldvay wrote the purest distillation of the "D&D experience" to date, but that's neither here nor there.
The main point is that while all of these TSR-era products are inter-operable and compatible, the best lineage is really:
OD&D -> Holmes -> AD&D -> 2e
(separately)
OD&D -> B/X -> BECMI -> RC
But putting Holmes within the Moldvay/Mentzer line does a disservice to both Dr. Holmes and to Moldvay/Cook/Mennzer, for no reason other than the shared use of the term "Basic."
Ya don't wanna be basic.
Finally, because it's fun, here's a post where Holmes reviews Moldvay:
From Dragon Magazine #52 by J. Eric Holmes Editor, first edition D&D® Basic Set rules The first thing to realize about the rules for the ...
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