Most Australians of my age, (yes I am old) know this story well. I remember wishing John did not smoke because I was worried about what it might do to his voice.
I was never really sure of the cause of his lack of ability to remember lyrics. I was hoping this might provide some insight - but it skipped over that issue.
Still, it is a wonderful trip down memory lane for some of us. Many famous faces join in to express their admiration for Jonny's talents and recount their encounters with a very down-to-Earth man.
I see it is now to be released on free-to-air TV (in Australia at least) so try and watch it if you can - or even record it if you still have that capability.