Universal products contain both truly universal products like batteries, but also products that don't have fitment data. This means you can have a product that says in the title it's for a Ford F-150 but if it doesn't have fitment data it will still end up in the universal product category.
Q: In my fitment filters I selected these specific vehicles... basically 1979 to 1993 Mustang only. Why are non-Mustang parts loading into my store?
A: Click on "Filters" and try selecting "Exclude universal fitment parts". It should look like this:
It may take awhile for your app to delete all the universal fitment parts… there are a lot of them! But this should definitely let you display only the parts from the makes, models, sub-models and years that you have selected.