Sure, as long as you're fine with NPCs that have no racial traits, and only represent completely generic individuals. If you want a NPC to have racial traits - say, to be a dwarf commoner rather than a generic commoner - the Monster Manual and DMG both suggest you add racial traits, which include ASI that matches (or very very nearly matches) the PHB versions under the core rules. But you don't have to, if you just want a commoner that doesn't represent any particular race (thus allowing them to represent a humanoid of "any race", as it literally states in the statblock).
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Yes, that is basically what I've been pointing out. They provide one approach to having NPCs reflect racial traits, and that approach points to the PHB or DMG traits. Which means that by the core rules, a NPC will have the same traits (or nearly identical traits) as the PHB race, to include ASI. You can always build an exception, but by definition, those aren't typical members of the species.
If your point is that if you want to give them a dwarven trait in the PHB you have to use the PHB... well, duh. That is blatantly obvious and also beside the point.
But also, man some of those traits are legitimately pointless for an NPC. For Example, Stonecunning. You are considered to have expertise in history when it regards stonework, but in reality, since NPCs will likely never roll for history, especially a dwarf for stonework history, it isn't worth giving to a dwarven character. Just like I don't bother taking a commoner and giving them Sleight of Hand to represent a street urchin picking pockets.
But, sure, I will admit that if I want an NPC to have a PHB racial trait, I need to refer to the PHB Racials Traits. And if I want them to have a magical item from the DMG I refer to magical items from the DMG.
The real point is though, that I am not required to use those, if I don't want to.
I don't think they've ever released errata for older books to include material that's been featured in later books. Seems like that would be arguably giving things away for free if they did.
Might be giving away things for free, but that tells us that the Orc, Goblin, Hobgoblin, Kenku, Lizardfolk, ect in the DMG were considered obsolete as soon as Volo's came out.
The ability score differences aren't particularly relevant, because the scores you see could have still had the ASI applied to them. Specialist NPCs aren't required to start with all 10s, and in fact probably won't, both for flavor reasons and so they can make sure they have the right attack bonuses, DCs, etc.
As for the other missing racial features, the Nilbog isn't exactly a normal goblin, so its lack of standard goblin features is easy to explain. The others suggest a difference for those specific NPC builds, but not a suggestion that a typical hobgoblin or kobold NPC, such as a commoner, wouldn't normally have those default features. You can't use exceptions to prove rules.
Flipping this around, care to explain why the orc NPCs in Volo's all do have darkvision, the Aggressive trait, and Intimidation proficiency? (Excepting the Nurtured One of Yurtrus, which is basically a mutant.)
So, we are now at the point where those Racial ASIs are not relevant to NPC statblocks because they can have any numbers, and likely will just have the stats they need for both flavor and having the right attacks and DCs. This was literally my point as to why Racial ASIs don't matter for NPCs. And, it pushes into the idea of floating ASIs. If I wanted to play an Orc Priestess in training, then if I wanted to emulate the Claws of Luthic I would need my Dex and Wisdom higher than my Strength, a bonus to strength is negligible for them.
And then you want to say that I can't use exceptions to prove rules, but what I am doing is showing that exceptions exist. By the way, look at the Hobgoblin and Hobgoblin Commander in the MM, also no Save Face Trait and "hobgoblin" is about as generic as we can get, since we don't have stats for "generic hobgoblin". Now, that was because Volos came out later, but again, if they didn't feel the need to update the Statblock, then are we really supposed to add these traits to generic hobgoblins? Or were they telling us that PCs and NPCs are different, by treating NPCs and PCs differently?
There is not a single Hobgoblin Statblock officially released that uses Save Face. Know what they do have almost exclusively? Martial Advantage. A trait that no PC Hobgoblin can access. Did you know that no NPC Bugbear statblock has a reach like a PC does? Did you know that they all have the Trait Brute, which a PC cannot access?
You can't claim that every single statblock is specialized and doesn't represent the "common folk" of the race, then turn around and tell us that the traits they are known for are specialized and not for the people who will become unique and powerful members of their race.
Sure, if you're building a creature that isn't a typical member of the species. That's different from building a commoner that has the racial traits of a PHB race.
How?
Mordenkainen's being even more recent than Volo's, of course. Also, the existence of different types of eladrin with different abilities actually goes back to 2E.
So even in 2e NPCs and PCs were not meant to be identical?
Really, you're suggesting that I'm not honestly suggesting that you could count the dragonborn varieties as subraces? (Personally, I probably would, since they actually have physiological differences - they're actually better suited to the term "subrace" than many of the other subraces.)
And sure, all ten of those dragonborn variants have the same default ASIs. If we accept those as subraces, that demonstrates how "there are subraces!" would not be an excuse to claim an entire species wouldn't have typical members, such that defaults couldn't be suggested.
It seems like a stretch to try and claim a subrace when no subrace is labeled. Especially since, per the lore, Dragonborn don't have their abilities because of a "true breeding" of their bloodlines. It is all muddled up to the point where two black scaled dragonborn who breath ice could give birth to a red scaled dragonborn who breathes lightning (and actually they are majority brown scaled I've heard).
It seems to me that you are only trying to claim such, so you can say that "not all subraces give different ASIs, so you can't use subraces like you were trying to use them," when this would be the only example, and it is relabeling something that has not previously been labeled as such.
The only nonhuman version of a standard NPC statblock we have in an official source that I'm aware of is the lizardfolk commoner, which 1) came out in 2019 and 2) doesn't really support either argument. The other two (goblin commoner and kobold commoner) are only on D&D Beyond and, as I pointed out, could be mistakes on D&D Beyond's part.
As for NPC statblocks not based on generic NPCs, those aren't typical members of the race and, as I pointed out previously, also do often have traits matching the race's defaults. And they don't really have a bearing on what a typical member of the species might be like as far as ASIs, since ability scores can vary.
I enjoy how you dismiss one of the strongest pieces of evidence I have as not supporting either side. The Lizardfolk Commoner is A) A commoner, letting them be a "generic member of the race", B) Officially printed and statted in an Official Product C) released after volo's and any changes to the Lizardfolk design that was entailed by Volo's and D) Completely unlike the PC version in Volo's. It does not have their iconic Hungry Jaws and it has a massively inflated strength score, despite Lizardfolk not giving a bonus to Strength. It meets all the criterion you have placed for what we should be looking for, and supports my postion that NPCs are not treated like PCs.
Then of course you dismiss other evidence as likely being a mistake, or the fact that they are NPCs and representing the unusual members of that society. Not like adventurers who are not unusual at all.
And with this:
Besides, I've been primarily talking about what their intention was as far as the core rules, not what might have came later. (I already granted it's possible they had changed their mind as early as Volo's; I just also pointed out that it's very possible they didn't.) As far as PHB races, I'm not aware of any examples of complete statblocks for race-specific versions of generic NPCs. In fact, every time we see a "drow commoner" or the like in the vast majority of books, they never tell you how to depict them. So they must assume you'd follow the guidelines in the Monster Manual for NPCs... which suggest applying racial traits (which include ASIs) when you want them to reflect a character race.
And you can keep believing what you want, even in the face of the evidence provided in the core rules.
It seems like all you are trying to do is prove that in 2014 they wanted all NPCs of a race to use PC abilities, based on the fact that they said if you want to use PC abilities for them you should use the PHB. Then acknowledge that in 2017 they had changed their mind on that, so that you can be upset in 2021 for them changing their mind YEARS ago.
I mean, I can concede that wizards intended in the beginning of the game that if you wanted to give a character hill dwarf traits that they wanted you to read the section on hill dwarf traits. That is the same as conceding that if you wanted to give them sneak attack they wanted you to read the section on sneak attack.
But, taking it that step further, and saying that if I wanted to have a dwarf NPC I was required to give them the PHB stats, ASIs and abilities and all? While at the same time acknowledging that the NPC monster blocks in the front of the book are specialized with their ASIs and may not reflect the generic member of that race? That is not only a bridge too far, but one that is unsupported since you immediately undermine it with exactly the point I keep making.
NPCs are not treated like PCs.