Trying to search local collections in Books

I’ve got a huge collection of pdfs on my iPad which I’ve been accumulating for years. They’re filed in Collections I created.

Alas, I’ve just realized with 18.1.1, Search in Books only searches the store for new content. This used to work and Search was context sensitive to what was being viewed. No more. Search automatically now switches context to one of the Stores.

I’ve tried searching for pdfs, which will temporarily show my Library, but any effort to narrow the results by entering the name immediately narrows the results to None from the Stores. Results of all 500+ isn’t useful.

So, how can I search my curated collections? Any availability to use metadata such as Source=Library Name:*name*.pdf?

Request to community at large: Assuming spotlight indexing, in concept if not in strictest sense, per OS is being deployed across the Apple ecosystem it seems there should be metadata keywords, attributes and wildcards which can be used in the various Search fields, i.e. Finder, mail, Books………..to tailor results

Please share, I can’t find it.