Since I seem to have started the complaining about the "documentary" I'll just add this bit in. Zimny was asked to film but told to "stay out of the way" of the creative process. So in essence, filming from some distance, he can't encumber what is happening around him and in front of him. And to track the development of the arrangement of a song might get boring in a hurry for those with little musical knowledge. Case in point, unlike many artists, Bruce has never released demos of songs. He's released finished outtakes only on the box sets. As co-producer of the film, it's his call about what he wishes to unveil about how he works.
Anyhow, I just wanted to play devil's advocate for my own comments after reading this piece on Backstreets.