Comment 5 for bug 1440304

Configuring metadata read from individual file formats is not something
that belongs in the core calibre program. Fortunately, calibre has an
extensive plugin framework. You can write a calibre metadata reader
plugin of your own to override the builtin one, if you want.

As for your OK and KO pdf files, as I said before, XMP metadata is used
in preference to the Info metadata always, *except* when the last
modified date of theInfo dictionary is newer than the XMP metadata
block. That is the case in your KO PDF. You need to make sure that
whatever program you are using to edit XMP metadata updates the last
modified date in the XMP block correctly. Use the calibre ebook-meta
program if you cant find any others.