Syncing Books throughout my Apple Device

I've upgraded my iPad to a 9th Gen iPad (iOS 17.4.1) and was able to migrate the Apple Book data (assorted PDFs and ebooks, some from Apple, others from non-Apple sources, plus my Collection categories) from my old iPad to my new through iCloud. Now I want to sync that content from the new iPad to my Macbook Air (2018, OS Monterey) and my iPhone SE (2nd Gen, iOS 17.4.1).

A little history:

When I upgraded my Macbook last year, the Apple Books data never got synced properly between laptop and iPad. My previous laptop had died, so I wasn't able to migrate data from old to new, nor did I perform a Time Machine restore because the previous Macbook was very old and I wanted to start fresh. Plus, I think I remember something about how I would lose the Apple Books content on the iPad if I synced it with the new Mac via cable, so I never did. I only synced / backed up that iPad via iCloud. Long story short - my complete Apple Book data resided only on that iPad.

Enter new iPad...

After migrating data via Quick Start and syncing through iCloud and via cable/backup to the Mac, I'm only seeing a partial list of items on the Macbook and thus also the iPhone.

Yes, I have iBooks and Collections syncing turned on on all devices.

What am I missing?

[Re-Titled by Moderator]