It's rather surprising, isn't it? In fact it turns out that the term was first used in print in 1984, but uncapitalised, in XSOLO. After that, I haven't finished reviewing 1985, but I know it appeared as the title of the world map in the Master Set. It was only at some point after that that it started to be used as the general name for the setting — and as you mentioned, GAZ1 still has The D&D Game World.
I find this very interesting, because it completely disproves the idea that early on Mystara was known as the Known World. In fact it's more like the (mid to late?) GAZ era that used that name.
I get that it's useful to people who prefer the earlier products to the later products to be able to draw a distinction, but Known World/Mystara is not a historically accurate way to distinguish them.
Further complicating the matter is the fact that although Known World appeared (first?) on the Master Set world map, it later came to mean just the area shown on X1's map. I'm looking forward to tracking the evolution of this term over the course of this project.
I believe that it was published in late (December?) 1980, and released in January 1981. But this is from reading sites such as The Acaeum. (I was only three at the time so I can't say I have first hand knowledge! )The Continent - X1 Isle of Dread Blue Cover (1980*) – I thought X1 was published in 1981, but my blue cover version states (c)1980...
This posed a quandary for me, too, in this project. I agree that we should trust Lawrence Schick at his word — he certainly deserves our respect, and there's no real reason to doubt him.According to this article, Lawrence Schick and Tom Moldvay did indeed use the name Known World when referring to their original home campaign played in Akron, Ohio:
It should be noted that the name Known World is not noted on any of the documents Schick provided so theoretically he could be misremembering whether this name was something they added originally or after it had been seen in print. I lean towards trusting Schick, but it is curious that it was not used in print untill long after Moldvay had left OD&D.Lawrence Schick wrote:We dubbed this setting the “Known World,” to imply there was more out there yet to be discovered, because we didn’t want to paint ourselves into a corner. It was our intention to use the Known World in ongoing open-ended campaigns run by multiple DMs, in which player characters could go back and forth from one DM’s game to another. Moldvay and I were already running our own campaigns this way, and we hoped to bring other DMs on board as well, so we’d all be playing in the same giant sandbox.
However... As you said, there's no mention of it in his documents, and the fact that the term doesn't appear in print until 1985 is rather puzzling. Were Tom Moldvay and Lawrence Schick still at TSR at that point?
My conclusion is that either the world was being referred to as the Known World (or possibly just the known world) behind the scenes from the start, or it was later "named" the Known World coincidentally.
Now I rather doubt the first option, because it seems to me that they didn't have much cohesion at that point, and the idea of a game world was barely even established — especially in the case of B/X and BECMI D&D. Most of all, the authors kept on changing, and there was very little cohesion from one book to the next.
Which leaves the second option. It's possible Frank Mentzer is the man responsible for the term, and it's also possible he had heard it from Lawrence Schick. Or perhaps he came up with it on his own, which would not be an entirely unexpected development given the generic nature of the "name".