You have an already populated gamelist.xml, but some media is missing that you didn't fetch/scrape. It is possible to filter games that do not have certain media.
2 methods are possible:
If your games list is already filled with media and you want to find missing media, you need to:
Check the box of the missing media(s) you wish to search
click on without
click on Or
Then click on Filter
If media is missing for a game, the game will be displayed in the database
You can do it manually by creating a query that will apply a filter on your database
Example: You want to search for games without Boxart or manual.
You will need to enter your request in the Request combobox. The request will look like this:
boxart_rom is null or manual_rom is null
Then click on the Filter button
You can reset the filter by clicking on the button No filter