If you convert the book after changing any metadata, that metadata is imbedded in the book file itself for most formats. A plugboard will embed metadata in the file sent to the device, but whether it get the metadata from the database or the book file (epub etc.) I am not sure. I like to make sure it is in the book so I always reconvert when I change covers or metadata. Then I know where I am.
Select book(s) click convert and hit enter
I have the keep original file tweak set to on in case I make a mistake, but your preference.
Helen