"0" next to material name, but still there after restarting blender?

I downloaded a skeleton, and it had a unique material for every bone. I only wanted the pelvis, so I threw away all the other bones.

However, Now I have an enormous list of white materials in my materials, all with a 0 next to them (which should mean they will be deleted when I quit Blender).

But I quit Blender, come back, and they are still all in the list, with 0’s next to them… …what gives?

I can’t understand, bones should not have materials assigned at all, it could be that they have custom shapes ( which are there even if you can’t see them neither in 3d viewport nor in outliner)

It was a skeleton mesh. XD Like a model of a skeleton. Not an armature skeleton. Oops, i forgot to clarify that.

Anyways, the 0materials did eventually self-delete.