NX The coating material remains visible in Teamcenter even after it has been deleted

1. Create a coating layer in NX and assign a coating material
2. File > Save > OK
3. Go to Teamcenter > Select the 3D Model Revision > click on "More Properties" on the summary tab
4. Click on "All Licenses" > Scroll down to the property "Coating material" > The coating material is visible
5. Go to NX > Delete the created coating layer and coating stack
6. File > Save > OK

Now the Material is still visible in Teamcenter.

This is working as designed. In Coating we could have multiple layers thus multiple coating materials IMM and even NX OOTB does not override the previous material like assigning to a BODY.
If you want to replace the material on the same layer you need to:
1- delete the layer from the Stack
2- delete the corresponding layer Material from the Material list on the part."

So when you want to delete the material you need to remove it from the Material list in the part about Material Library Manager and save the part.