We have fallen way too deep into the rabbit hole. I feel bewildered by all the specific breaking down of various editions' lore. I don't see much effort to break down what value continuity has, or why additions to lore are in any way less disruptive than carefully curated changes to lore.
Before - or, perhaps, as part of - establishing what value continuity has, we need to establish what value lore has.
This is the point, for me, of the debate about doppelganger "lore" in the 2nd ed Monstrous Compendium/Manual. That is, whatever value lore has, being told that doppelgangers are grey and hairless and sometimes follow people to inns doesn't serve that value.
You said "A player who started with any version of D&D should know what an orc is. In play it should feel like an orc. When reading the monster manual it should noticeably look like an orc. Any changes - whether through addition or transformation should attempt to stay true to the narrative hook and role of the orc so that it remains familiar to us." I agree with this, but I simply don't think that the colour and hirsuteness of doppelgangers in their "true form" are relevant to their "narrative hook and role". (Googling turned up what seems to be a pirate website of the 2nd ed monster books. The illustration of doppelgangers - maybe by Tony DiTerlizzi - seems intended to depict them in their "true form" but neither has an exposed brain and one has a thick head of hair!)
If the value of lore is to provide a narrative hook and role, then that makes it clear how more can be less, because it dilutes what is salient (in my view being told about the "true appearance" of doppelgangars does this); why addition is not neutral or unproblematic vis a vis change; and why change can be worthwhile, if it better clarifies or hones in on that hook and role.
Lore should also sometimes be exciting or even confronting. It should make you think about some element of the fiction in a way that you otherwise woudln't have - to shed some new light on what it means to have a certain hook or role. It shouldn't just be a lullaby, or the written equivalent of comfort food.