Tags are saved in a .xml file beside your video files. (e.g. VIDEO_TS_ifo_JRSidecar.xml)
I don't no if I understand what you mean.
If you want to check you could change some tags and then check the .xml file in notepad. There you can see the changes.
I use more tags for my videos and the only thing that is not updated automatically is the "year" tag. If I've changed and/or added videos I select the new videos and right click "update tags from library". That way I'm sure everything is updated, also the "year" tag. Don't know why it isn't updated anyway, asked for that but never got an answer.
The tags I use are: "Title", "Original Title" (for titles like "The Good, The Bad and the Ugly" = "Il Buono, Il Brutto, Il Cattivo") "Actors", "Director", "Genre", "Year", "Comment", "Catalog #" (for my physical discs that I've stored in cd-boxes with sleeves e.g. B 182), "duration" (auto). I also use "album" and "name" for sorting reasons and for properly naming my folder.jpg. For TV Series I use "series" and "Seasons". With these tags it's almost impossible to not find a movie I'm searching for.
If you are just starting I would recommend using a few more tags than you do now. Hope this helps.
Theo