Hi and welcome to the forums and community.
The audit tool in Launchbox isnt designed for this purpose, it is designed to audit things that are already inside of Launchbox. So it will show games not linked in our database, or games with no images, or no videos and things like that, it isnt designed to tell you what you do or do not have for a system. Those things are often difficult to do, especially as lists will often vary in the number of officially licensed games and the like. There are programs out there that will match dat files to the files you have, but again that relies on the dat files in question being 100% accurate in the first place.
Ill be honest and say if it was me, and there was one game missing and i couldnt see which one by eye and knowledge id probably just shrug and say, well it cant be that good anyway. but i get that some people like to know they have everything. You will unfortunately need to look for a third party solution in order to ascertain that im afraid.
At the end of the day Launchbox's intention is a launcher for games hence the name, while it will of course catalog your games that you import, it isnt designed to be a be all and end all of very specific data like that.