Each score can't be a book, as it's included in a book.
>So you can't use boookOutputSuffix or bookOutputName:
>http://lilypond.org/doc/v2.17/Documentation/notation/output-file-names#index-_005cbookOutputName
>
>You probably want to ask for the same feature for bookpart, i.e.
>bookpartOutputName and bookpartOutputSuffix
The feature already works. If you specify \bookOutputName inside of a
bookpart, that takes preference over the \bookOutputName in the book
without disturbing the book's own idea of the output name.