One of my favourite positive doctoral viva stories was Wittgenstein, who presented "Tractatus Logico-Philosophicus" as his dissertation, which had already been published and was already considered a masterpiece. The report was something like "We consider the work of Mr Wittgenstein to be the work of a genius. Nevertheless, it fulfills the criteria for a Cambridge doctorate".
Edit to add: The actual quote (which I just found) was from G.E. Moore (Bertrand Russell was the other examiner): "I myself consider that this is a work of genius; but, even if I am completely mistaken and it is nothing of the sort, it is well above the standard required for the Ph.D. degree."
Edit to add: The actual quote (which I just found) was from G.E. Moore (Bertrand Russell was the other examiner): "I myself consider that this is a work of genius; but, even if I am completely mistaken and it is nothing of the sort, it is well above the standard required for the Ph.D. degree."