[Ken Maltby]

Are the shelves calibre creates and manages in the stock Kobo database included in the "metadata.calibre" as tags? Perhaps you could make a tag in calibre and apply it to the books in one of your shelves and delete then resend the books to your device, to see if the tag appears in KOReader.

Another approach might be to have calibre add a code to the book/file name, that KOReader's "Find file" function could use. You could have it put at the end of the name and would only show in the File Manager listings if you have set the font size real low, but would work for the search. ( I never figured out how calibre and its "Plugboards" work to impact the names. You might ask over at the calibre forum.)

Luck;
Ken