From the Foreward of the Players Handbook (AD&D)...The fundamental thing to understand is that 0e and 1e were never designed to be complete systems, or designed to be complete- they were always intended to be used as toolkits. As detailed further below, it is only with that basic approach that you can begin to make sense of early D&D's design principles.
...and from the Foreward of the DMG:This is the second release of the ADVANCED DUNGEONS & DRAGONS series, and is designed to be a player's book in every respect - giving you all the background you require on the game system, as well as all the information you'll need to go adventuring.
There was absolutely an intent, by the designers, that these books would be a comprehensive, cohesive, and capable set of tools from which you could run D&D with no other materials required. They failed miserably, but that was absolutely the intent. They were intended to be all you needed, not just a toolkit.This book ... is your primary tool in constructing your own "world", or milieu. It contains a wealth of material, and combined with the other workd of ADVANCED DUNGEONS & DRAGONS (the MONSTER MANUAL and [/b]PLAYER'S HANDBOOK[/b]) gives you all the information you need to play AD&D.
Unfortunately, the books contradict you, as do many of the interview notes from historians of the games when they've interviewed those designers.Please note that while I am using information learned from various great sources, I don't have my books handy, so I will be doing this mostly from memory.
The books were intended to be a be all perfect compilation of the rules. They failed, miserably, because the designers massively underestimated the difficulty of the task they undertook, but the books were intended to be all you needed.