The Project Gutenberg FAQ - V-36

V.36. I have one physical book, with multiple works in it (like a collection of plays). Should I submit each text separately?

If the works are clearly separate, stand-alone texts, and are long enough [V.17] to warrant inclusion on their own in the archives, then yes, you should, and you may also submit a "complete" version as well, if it seems appropriate. This most commonly happens in a collection of plays, though essays and other works may also fit the criteria. Collections of poetry rarely do, since most poems are too short to submit as stand-alone texts.

Sometimes the book includes a preface or introduction or glossary covering all the works in it. In this case, you can decide whether to include these with each of the parts, or save them for the "complete" version.