If none of Claudius' works survived, including his autobiography, from what sources did Graves get all his personal material (such as Claudius' hatred/love for certain people and other important conversations) from? I do understand that the book is historical fiction and I do know that Claudius' writing is seen in other contemporary historians but is it seen to such a strong degree that Graves can use it to constitute Claudius' character and persona with?

A simpler version of what I am asking would be "how historically accurate is Graves in depicting Claudius' personal traits/tastes as well as conversations (Augustus to Claudius,etc) in the book?".