Here I must engage in full disclosure: I have done freelance work on several of DK’s books about comics, as well as comics encyclopedias for other publishers. So I know how monumental a task researching such books can be, and salute The Vertigo Encyclopedia’s author Alex Irvine, who, oddly, is credited on the cover but not on the book’s title page.
At least in the past, DK’s guides to comics characters like Batman and the X-Men were officially part of its Children’s Books division. The Vertigo Encyclopedia is most definitely not for kids: leafing through the book, I came across not only the F-word, but also an example of full frontal nudity and a reference to “pansexuality.” Irvine also takes a more sophisticated approach to the material, listing the credits of Vertigo creators, outlining major storylines, and even pointing out literary themes.
There's more, and Sanderson also reviews Robert Greenberger's Essential Batman Encyclopedia (which I have, and think is excellent).