You may also want to consider this, if your files are already in the VirtualDJ database:
After a file is loaded into the database, meta data is taken only from that library. Any later changes or additions to a file made in an external tag editor are ignored.
However, there is a procedure to update the VirtualDJ database to include external changes. It's called Batch -> Reload Tags and was posted here by @LyricsLover. See his reply linked below for a screen shot . Scroll down, towards the end of a long thread: Set rating for import in VirtualDJ