This recent release from the Northern Illinois University Press is not legal history, but its basic premise -- that authorship matters -- seems relevant to the field: Who Wrote That?: Authorship Controversies from Moses to Sholokhov, by Donald Ostrowski (Harvard University Extension School). A description from the Press: 
Who Wrote That? examines nine authorship controversies, providing an introduction to particular disputes and teaching students how to assess historical documents, archival materials, and apocryphal stories, as well as internet sources and news. Donald Ostrowski does not argue in favor of one side over another but focuses on the principles of attribution used to make each case.
While furthering the field of authorship studies, Who Wrote That? provides an essential resource for instructors at all levels in various subjects. It is ultimately about historical detective work. Using Moses, Analects, the Secret Gospel of Mark, Abelard and Heloise, the Compendium of Chronicles, Rashid al-Din, Shakespeare, Prince Andrei Kurbskii, James MacPherson, and Mikhail Sholokov, Ostrowski builds concrete examples that instructors can use to help students uncover the legitimacy of authorship and to spark the desire to turn over the hidden layers of history so necessary to the craft.
H/t: New Books in History, where you will find an interview with the author.
-- Karen Tani