>>95979438
I'm less sure of the exact circumstances of that one, but IIRC it's known from two or possibly three facts: firstly, the players on that second occasion encountered the evil dwarf Obmi, a known inhabitant of level 3; secondly the label "Obmi" can be just about made out in the bisected circular room labeled "7" in the lower right (see pic related reconstruction; I really wish I could relocate the blog where these were posted), and the possible third is that the players may have been told they'd ventured to level 3 by Gygax after the fact.

More circumstantially the description of this level also resembles that given by Gygax for level 3 in various early publications.

Finally, you are of course correct that 2e is not an OSR game, and as such, is off-topic for the purposes of this general.

>>95979459
This anon is also extremely correct.

>>95979466
kekk