Good question!
There don't seem to be archived copies of the documentation for prior versions. This has been a longstanding issue: in the past, the ebook version was available simultaneously for both the beta and release versions, but there hasn't been an ebook version lately. You can try to use archive.org.
Nested protocols are a new feature added to the language in SE-0404, and this part of the book was only updated a few weeks ago. Indeed, in Swift 5.9, you'll need to not nest the Delegate.