So, after yesterday's post about the first Basic Set, the Holmes Blue Book, let's recap by saying that the Holmes set lacked vital rules for playing beyond a certain point. It wasn't a working but simplified version of AD&D (e.g., missing rangers, some spells from each level, some monsters, some treasure, etc). Rather, it stopped working entirely at a certain point.
The next Basic Set to come out was the 1981 Red Box, "Moldvay Basic," or "B/X." The reason for the "X" in "B/X" was to stand for the Expert Box that a gaming group could move on to once they had exhausted the resources of the Basic Set.
Now, if you've been keeping track of my focus so far, you've probably already guessed the point I'm about to make. The Holmes Basic Set graduated the players up to Advanced D&D. The Moldvay Basic Set (which went to level 3 just like the Holmes set) didn't. It graduated you to something that was effectively a parallel to Advanced D&D, because the Expert set (which I just looked up for information) went to level 14. At this point in time there were two versions of low-to-high-level D&D.
I don't have much to add about 1983 "Mentzer" Basic, also called BEMCI because it contained Basic, Expert, Companion, Master, and Immortal rules. I never happened to play this edition (I was a proud-to-play-Advanced-snob even by the time of the Moldvay set), but the Mentzer edition isn't relevant to this particular history because it's essentially a continuation and a culmination of the trend started with the B/X sets -- the creation of a parallel D&D game.
Although there have been other D&D Basic sets, the continuum from Holmes to Mentzer set the stage for two different approaches to Basic Sets, which now that I have established, I'll get into in the next installment of this series. Stay tuned!