For me it was in 1984, shortly after DSA/TDE was released in Germany. Talking about the game on the school bus got me introduced to a DM looking for AD&D players. And one of the players was a DM for D&D ...
p.s. My memory being what it isn't, I could be wrong, and 1988 is the peak caused by 2e; in which case I can't explain 1992. Either way, one of those makes no sense.