The idea that a game about film-noir style detectives who are out solving crimes and getting in scrapes with cops, criminals, and jealous spouses is 'lacking rules' because it doesn't have a means to satisfactorily resolve World War II battles (or even the whole thing!) in real time is just silly, as is saying that Kids on Bikes is missing rules because it doesn't have a system for handling the war in the Middle East (whichever one is contemporary to your setting). They're clearly out of scope for the game, and even your example doesn't come up routinely in a game.
So let's take that at face value. First, I can never imagine myself buying a game about film-noir style detectives who are out solving crimes and the rest, because off the top of my head I can think of zero examples of the genre of "film-noir" style detectives where the detectives are an ensemble cast who work together cooperatively. RPGs are in my opinion social, and you're taking as inspiration stories that are not typically social and cooperative. What you are doing is extrapolating into setting, which is say the 1930s that never was, and setting a street level super-hero story there and perhaps not even realizing it. And if I start thinking about that, then the sort of thing that comes to mind for me is "We're no angels", a dark comedy about three escapees from Devil's Island who rob a family during their escape attempt but catching a sudden case of conscious, decide instead to help and protect the family against the forces of evil. And that's set in a fictional Cayenne in French Guiana, so the very very first thing I'm going to be asking of your hypothetical system is can it do "We're No Angels". And it's a small jump from there to WWII for me, as something like Casablanca shows. Because if I do a Casablanca scenario in an RPG, and it ends the way it did, the next story for the characters is the French Resistance in WW2. And maybe I don't even intend that, but it works out that way, and now what? Unlike a movie, the story doesn't end. Players are if they are having fun wanting to go one with characters they love and plots that there are digging into.
Kids on Bikes set in Iran or Ukraine or something would be amazing.
But even if we ignore how wildly out of scope contemporary mass combat is for a game about children on bikes, if a game has rules for combat then the game does have rules for mass combat. You just use the combat rules. You may not find it convenient, but "It's cumbersome to do X under the rules" is simply not the same as "the game doesn't have rules for X".
Now you are arguing my point for me. Because in my original post on this topic I said that from one perspective no rules are ever "missing", because obviously you could just roll 80,000 D20's (or whatever you needed). In fact, this goes back to the discussion of Celebrim's World Simpliest RPG where I discussed the simplest possible set of complete rules, and why we have rules for RPGs in the first place. Yes, technically, a game that resolved every proposition with a coin flip has a rule for everything, but that really misses the point.
AD&D does not have rules for when someone who isn't a thief attempts one of the thief skills, thus it is a missing rule, there is no rule to follow for what happens there.
The rules certainly do not imply anyone can attempt one of the "thief skills" if they are not a thief. There are no rules in place for what happens if someone attempts to cast a M-U spell if they aren't a M-U either, nor are there any rules for what happens if someone petitions a deity for a spell who isn't a cleric. Yet this doesn't seem to raise the same sort of hackles. It's "obvious" what happens if someone who isn't an M-U attempts to cast a spell from a spellbook. The truth is really that in one case you think there is a "missing rule" because you don't like the outcome of applying the rules, where as in the other you've probably never even thought about it because you don't mind the outcome of applying the rules.
Inventing a rule is inventing a rule, and what you've done here is invent a rule.
I have not. It's not inventing a rule to say that failure is automatic if you attempt to cast a M-U spell when you aren't an M-U.
is contradictory to the way I've seen it played, the way most OSR advocates say it should be played, and the way people like Gary Gygax described it being played, so it's not like there's an obvious answer.
That I agree with. I've got a whole thread on this in the "old systems" forums about the fact that AD&D never got around to creating a unified answer to the question of non-combat propositions even though everyone including the designer seemed to understand that the rules were insufficient here. No one seemed to agree on what the rules should be, but everyone seemed to agree there needed to be more of them.
