Manuscript Preparation, Copyediting, and Proofreading
Q. Can the running heads in a multivolume set of books be the title of that particular volume rather than the overall title of all the volumes in the set?
A. Yes. Where running heads are concerned, there are few rules per se, only some useful conventions that depend on the book: “The choice of running heads . . . is governed chiefly by the structure and nature of the book” (see CMOS 1.12, which lists some common configurations). Consider the reader, and if your choice makes more sense than the alternatives, run with it.