[HarryT]

Let's be clear about definitions here.

Your book as a whole cannot be reproduced without your permission, because you've written an introduction for it, and that's unquestionably protected by copyright, but there's nothing to prevent anyone from copying the text of the Shakespearean texts from your book and re-using those, because the Shakespeare remains Shakespeare - you have not made any creative changes to it.

A derivative work is something like "West Side Story" or <shudder> "Pride and Prejudice and Zombies", where a public domain work has been transformed into a completely new work. You have not transformed Shakespeare's work into something different: it is Shakespeare's original work, with the only changes being corrections to the text (which, as we've already explored, do not gain you a new copyright).

So, can you put a copyright notice in your book? Yes, certainly. Will that prevent anyone from re-using one (or all) of the Shakespearean texts in your book? No, it won't, although it will prevent anyone from simply copying the book as a whole.