@Ckepper , the person behind the Book Creator, "would be interested in retrieving a backup of the complete books namespace for future reference (my idea is to use this data as part of an auto-suggest feature)."
The namespace was deleted from en.wp in 2021, and there's a message saying "individual books will be restored upon request", but we're talking about many, many books here.
If anyone wants to volunteer to make this happen or provide advice, that'd be appreciated.
(I've already investigated internally and I've been told "mass undeleting (temporarily) could make our DBA's cry", FWIW.)