thedungeondelver
Adventurer
Curious, why do you exclude the Rules Cyclopedia?
Essentially because one, it's not "basic" by name any longer and two, it added some things (prestige classes) that really mark a sea change for me.
Note that I don't say it isn't D&D, just not basic D&D.
Mentzer Basic, post EXPERT D&D is the same way. You get into the COMPANION, MASTERS, and IMMORTAL rulesets and things just really start to go far afield from the stock and trade definition of "basic D&D".