Gustave,
The tragedy of the last third is that actually "third" is just an approximation, and in reality those final polishing steps can drag on forever if you allow them to. Sometimes an artist has to know where to cut and say "this belongs to the world now, not me."
But as a matter of practice I have found that it's nice, on occasion, to go back to old pieces and revisit that last third one more time in light of my new knowledge. It's a chance to connect to something old and create something new at the same time, and I always learn something from it. There have even been a couple pieces I have looked at and realized that I enjoyed them much more, and believe they were both technically and spiritually better, than the stuff I currently produce. That's a humbling thought and keeps me from getting too lazy and routine.
One thing I cut from this piece, to save length, was a fourth principle which I refer to as "abstraction." Basically, you can take a finished piece and move backwards in the iteration process, and then redo the final steps. It's a great method for troubleshooting but also for discovering how you have changed. I have seen many artists do it; they revisit old pieces, take their original concept, and do a remastered version of it to see how they have improved. It's always a powerful double-take. I'm not sure if I have seen many writers try the same, but someday I may, myself, just for the joy of it.
J