Interesting comment about plays in the theatre. There is a story and I may not recall exactly right but this is the essence.
A famous actor (I think it was Laurence Olivier) was in the middle of a longish run and, one evening, everything went really well, mainly because he had been stunningly good. The cast members were elated and gathered for a post-performance celebration. Soon, it was realised the actor wasn't there, so someone went looking and found him in his dressing room. Whilst everyone else was on a high, he looked a bit gloomy. Asked why, when everything had gone so well that evening, he replied (something like), "You don't understand. I don't know what did it". In other words, he would like to repeat that great performance but couldn't work out what he would have to do, specifically, to achieve it.
My point is two-fold. (1) Even with a well-rehearsed performnace, you can have good nights and you can have really, really good nights. (2) Performance in a live show can depend on so many different factors, some simply beyond our comprehension. It just comes together perfectly and that's the magic of live entertainment.
Getting back to the actor's story. Does it mean that the audience members who went all the other nights were short-changed or "disrespected" in some way? No, because, with a live performance, the dynamic will change each and every night. Now, I know that's not an exact match for the "Bob and Mark" situation but there are parallels.
Dylan, based on his shows over the last 25 years, does not seek simply to replicate a rehearsed show, night after night. Maybe, this is his nature - who knows? Rather, he seeks the "moment" and to re-present his songs in new ways. Sometimes it works, sometimes it doesn't, but it is admirable that he keeps on trying. Rather like the jazzmen of old, one might say, he seems anxious to avoid getting in a musical rut.