I'd suspect something in the 1e, B/X, 2e era for exploding it, also 5e for the ridiculous reach it has had.
I'm not sure 3e really expanded the market significantly. I think it maintained the market well, but I don't think it gained much ground.
I got my copy of Moldvay Basic in a WALGREEN'S.
I got a number of my AD&D books from SEARS.
In those days, D&D had retail penetration it doesn't even have today.