I've probably said before but I attended all four shows.
I wrote some notes about the shows in ISIS magazine and, when one of the bootleg albums appeared, the perpetrators had used my words as the liner notes but I didn't even get a copy of the bootleg set. And still don't have a copy.
Anyway, I have managed to dig out my notes on the incident in question and here's what I wrote, as an aside at the end of my piece:
As the band started the introduction to One More Cup Of Coffee, Dylan went across to Tony Garnier and asked, "What's the first line? I forgot". Garnier was also unsure. A girl at the front called out, "Your breath is sweet" and Dylan was away; he really went at the lyrics, seeming to thank the girl by his movements. Then, on the second show, he came out after the main set, walked up to her, bent down and asked, "What's the first line of I Shall Be Released?". On being told, he said, "Oh wow!" and did the song. The latter could have been a test, of course, but the episode raises an interesting possibility. When we find Dylan deviating from the cue sheet or seeming to start one song but actually beginning another, perhaps (just "perhaps"), he is simply singing a song whose first line he can recall at that precise moment.