It is often claimed in the historical literature that Plato's teachings were divided into the written documents (his famous books, like The Republic, The Laws etc) and oral teachings (what Aristotle called the "unwritten doctrines") . Some scholars even claim that the best and most important part of his philosophy was precisely the oral one, delivered in the Academy, while the dialogues were merely intended for philosophical dissemination. This hypothesis is supported, among others, by the works of the Italian historian Giovanni Reale.
This view, however, has been disputed by other scholars. In The Cambridge companion to Plato, for example, the author writes:
There is no evidence to suggest that there was a large body of oral doctrine constituting a complete system that would underlie, explain, or undermine the dialogues. [...] There is no evidence to suggest that Plato or anyone else took his oral teaching any more seriously than he took the dialogues.
Has there been recent studies on this subject? Is there any compelling recent evidence for – or against – the hypothesis that the "unwritten doctrines" were the main part of the Platonic philosophy?