When I first started roleplaying, back in 1975, there were no modules. Instead, people spoke of "dungeons" - as in, "Say, we're going to play in Steve's dungeon on Saturday - want to join us?" The idea of going on an adventure was firmly inside the frame of a larger campaign. Some people had elaborate set-ups, with kingdoms, history, background - even different races to play. Others were focused on the site of adventure; everything else was superfluous. If players came and went, so did their characters.
So when I picked up a copy of Keep on the Borderlands just the other day at Frugal Muse Books, I found myself remembering some of the reaction of "old-timers" to the idea of stand-alone adventures: "why would you want that? I mean, it's not even written for your campaign." Up until 1977 or so, almost all of the material produced for D&D had been published in The Strategic Review, The Dragon, or Judges Guild material (the latter being more recent). Which resulted in lots of interesting monsters, magic items, elaborations on the rules, and all of it got picked apart and then kitbashed by referees for their own games. What this meant for the players was that the narrative of adventure emerged from play, and wasn't predetermined by a series of modular pre-fabricated interactions.
So it seems to me that the period of 1974 to 1977 could be marked as being fundamentally different from roleplaying after 1977. It's that kind of gameplay I want to see explored further in the Old School Renaissance. Put another way, think about this - how would you design an adventure to share with others that didn't have a "greased rail" approach, like so many adventures written at the time?