When installing the Noesis unity package did you import the samples?
We only define that label for the textures used in the samples, so if they are not imported the Noesis label won't be created in the project.
Maybe we can add that label to any of the plugin editor images so it is always present.

Thank you, Sergio. Importing assets was the needed fix. For future reference, is there a specific file in samples that I may import to get the label?

You can manually create the label.
Just select any of your images you want to set for premultiplied alpha, click the label button in the inspector and write "Noesis" and hit ENTER.
It will add the label to the list and make it available for the project.

Does that work for you?

yes, thank you!