As far as can be gleaned from all available sources its was just hashed out verbally between Lucas and Kurtz.
So the idea that he had the story already written for 9 films is just flat on its face bullshit if not a complete and utter lie.
In Lucas binder of scripts there is no outline for 1-3, or 7-9.
Prior to putting pencil to paper in nov 1 1994 there was no backstory for star wars except in Lucas mind.
His general idea for the prequels changed between 1983 to 1999-2005.
The bad mother and good mother idea vanished. The love triangle vanished.
The slow seduction to evil of Anakin by the Emperor vanished.
Anakin being a good friend and great starpilot vanished.