QUOTE
You honestly believe that Lucas had all six movies planned out, despite the inconsistencies?
Personally, I don't think so. Of course, I am coming from another perspective. I myself am a writer, despite never actually having published anything, and several people I know are writers, including one friend who has managed to produce a movie.
The writing process, at least how it works for the rest of the world, if not GL, is that one comes up with the characters, the story and situations they are in, and the writer comes up with how the characters and everything fit into the story, much like an outline - i.e. Character A falls in love with Character B, but Character C, the villain, captures A, and B has to rescue A. Along the way, B decides to hire D, E, and F, and B's life is complicated by a strong attraction to E, while F might actually be working for C. The final confrontation between B and C for A's freedom comes up, and B is surprised to learn that A is now sympathetic to C's cause, and now B has to figure out how to win A back over to the "right" side.
It is while in this stage the author can tweak the thing, and change what happens, change character names, and even drop characters that add nothing to the plot, or work to strengthen the relationships, or the tensions between the heroes and villains. There are also plot twists that can be made, as in the example above, that F is actually an undercover agent, trying to take down C's criminal enterprise and D is a traitor.
That is a pretty simplified view of the process. I have had trouble in the past with villains that were far too powerful, so I would have to work on some sort of vulnerability for the hero to exploit, or characters who were too boring, and have to spice them up.
The point is, in the outline/plotting phase, if something is changed make sure that any inconsistencies are dealt with! If it is established that B is actually the son of F, make sure that IF that known fact changes, such as B's mother lied to F about B's paternity, it is done so in a consistent and interesting fashion. Or, if the author decides to eliminate a character from the story, such as a problem with too many characters, then the now-missing character's function does not upset the story. Such as, "Who the hell is going to pilot the ship now, since I did away with Character G?"
Someone much wiser than I (and I wish I could remember the name of that someone!) once said, "Of COURSE truth is stranger than fiction, fiction actually has to make sense!"