In the Attribute manager you will see a little tick next to any surface (or other attribute) that is being used.
Don't delete those but it should be safe to delete others.
But even better is in the Surface Settings dialogue you can 'Delete & Replace' any surface (same for many other attributes too) so not only will they delete but they will change to any other surface you choose so you won't get the 'Missing' surface.
Barry.
One of the forum moderators.
Versions 6.5 to 27
i7-10700 @ 2.9Ghz, 32GB ram, GeForce RTX 2060 (6GB), Windows 10
Lenovo Thinkpad - i7-1270P 2.20 GHz, 32GB RAM, Nvidia T550, Windows 11