A few entries ago I was trying to trace the source of the idea that Merlin created a 'cheating castle', as claimed by Alexander Oldknow (some time between 1660 and his death in 1665) in Lucy Boston's book The Children of Green Knowe. What I've only just noticed - and please picture the handpalm here - is that, earlier in the book, when the modern-day characters discover the 17th-century children's toybox, it turns out to contain a number of books. These include the Aeneid, Aesop, Malory's Morte, and a couple of other books I don't recognize: The History of Troy and Merlin the Sorcerer. Presumably the last is the book where they read about Merlin and his castle.
It's progress, of a sort - but I have no idea what book this is! The British Library, at any rate, has nothing under that name. (The Troy book is equally elusive, for that matter.)