It is all about perspective.
If you want to find the unwanted: Run FROM the place they should be:The sub Library.
Why do you call it a SUB? It is a separate Library that was spun off from a different one. I also have a 'Magazine" Library because it has a different STRUCTURE (custom columns) than the MainLib.
OTOH a VL is a SUB VIEW (but you can't remove books, only adjust the filter to exclude)