On the most recent episode of A More Civilized Age, the crew muses about how much of the Clone Wars was known, planned knowledge by George Lucas at the time of Heir to the Empire's drafting.
This wouldn't be without precedent; Lucas's early drafts are filled with names, concepts and characters he would use almost thirty years later, from "Mace Windy" and "Kiber crystals" to my favorite: that C-3PO was, at some point in his past, rebuilt by a little boy in a junkyard.
But as far as the evidence suggests, the ultimate canon nature of the Clone Wars was developed late and kept extremely close to Lucas's chest. The first mention of the Clone Wars came from the third draft of Star Wars, where Luke Starkiller is saved from Tusken Raiders by the legendary Ben Kenobi1. In this iteration, not only does Luke know his father served under General Kenobi2, but that he knows Ben's Diary of the Clone Wars by heart. A far cry from where the canon would land! 3
The idea of revisiting the Clone Wars came up during early story development for The Empire Strikes Back; in particular an early concept for Lando Calrissian was that he was a Clone, and that's the reason for his bad reputation. But even then, details on the Clone Wars were kept vague. From a story conference with Leigh Brackett in 1977: “Maybe he could look human but not really be human. He’s possibly a clone. We talked earlier about the Clone Wars. The Princess doesn’t trust him because of that; Leia might refer to him in a derogatory way. If we set him up as a clone, maybe in one of the other Episodes, we can have him run across a clan of them who are all exactly like him. We won’t go into the whole mythology of where they came from or whether the clones were good or bad. We’ll assume that they were slightly weird in their own way and were partly responsible for the war. We’ll assume that on these planets of clones, there are many countries, say about 700 countries and he’s from one of the ruling clone clans."
Return of the Jedi wouldn't revisit the Clone Wars at all, but it is worth noting that fan speculation at the time with rife with hypothesis about clones. Darth Vader being a clone of Luke's real father was a popular explaination for how the revelation at the end of TESB could make sense; the notion that the Emperor was possibly the clone of Obi-Wan Kenobi was another one.4
The details of the Clone Wars were kept vague and conflicting late into the EU; some sources put "decades of peace" between the end of the Clone Wars and the rise of the Empire; others had Princess Leia and Boba Fett as active combatants during its heyday. In a very odd wrinkle, often the Clone Wars were conflated with Mandalorian-Jedi wars-- the Clones as some kind of diabolical plot by the Mandalorians to infiltrate and overthrow the Jedi from within.
...which, actually, raises an odd question-- there's a tremendous amount of content in The Clone Wars TV show about The Mandalorians. Could their inclusion in the story be the echoes of whatever Lucas's original notion of the Clone Wars was? Wouldn't it be ironic if the one detail of the Clone Wars that persevered across the decades wasn't even about the clones!
-
“You’re General Kenobi?!? The Jedi Knight? The commander of the White Legions?”
-
“General Kenobi was my father’s commander, and he is probably the greatest of all the Jedi knights . . . or at least my father thought so.”
-
This version of Kenobi also has a robot arm, and can no longer connect with the Force, as his Kiber Crystal was stolen by Darth Vader in the battle where he betrayed the Jedi.
-
Apparently only so many people could wear hooded robes in the galaxy.
