Damn, they're a lot easier to clean if the dish surface inside has some sheen.
I'm not sure when my Corning Ware vintage casserole surface lost it's sheen. When Corning Ware casserole dishes lose their sheen/glaze, baking fumes lock into the surface.
Once you have a clean shiny surface (I hope with my ebay bought P-10-B dish), EZ OFF Fume Free cleaner out performs Baking soda. Hands free cleaning. I coat the whole dish with EZ Off occasionally.