I've just got a reply from foobnix with a beta version that addresses and perfectly solves my
prior post.
Using the .OPF file that calibre creates for each ebook, this version properly maps all of the relevant metadata, regardless of the ebook file format.
I've tried this version with the files stored directly by calibre (testing for a future cloud sync between devices) and the files created with the "Save to disk" option, with identical results.
I shall take again this opportunity to thank foobnix for his prompt reply and excellent service.
I remain very grateful,
[INCANUS]