I disagree, 2e at the very latest.D&D has been self-referential since 3e.
If not from the very beginning. D&D is often described as having defined it's own sub-genre of fantasy. It initially, like 0e, tried to capture archetypes from the broader genre, but, at, like one whole class per character - Ranger for Aragorn, Cleric for Van Helsig, Monk for Kwai Chang Caine - and when that clearly was never going to work, just hunkered down and worked with what it had from Men & Magic through Eldritch Wizardry.
3e was probably the first edition that wasn't entirely self-referent, and occasionally tried something new. 4e, of course, not even Essentials, just the first 2 years of 4e, was the last.