I asked Frank Mentzer:
Thorf reports that the first definitive usage of the name "The Known World" appears in your 1985 Master Set world map. Yet Lawrence Schick and Bill Wilkerson seem to recall referring to their home campaign as the "Known World" even back in the 1970s. Can you shed any light on this? Which scenario best matches your recollection:?
A) Did the TSR folks who'd worked on D&D in 1981-1984 (e.g. Moldvay, Cook, Marsh) use that as a "behind-the-scenes" "intra-office term" for the world throughout the B/X and early BEC(MI) era, and then you finally put it on a public-facing map in 1985?
B) Or did you yourself invent that moniker for the 1985 map?
Frank replied:
"It came from Ohio, Moldvay-Schick. 1980-82 roughly. Law & Tom moved on, but it stuck."