Kitty - When dies are prepared to have the "cameo" frosted appearance on the devices, the entire die is acid etched and then the fields are polished smooth. I suppose they can etch the devices individually, but that is risky. Some times the polishing of the fields accidently gets to the devices. When a die is mishandeled it might have to be refurbished or just needs to be refurbished due to striking wear. Any of these repairs can result in polishing in the detail of the devices. Your hat example is a great variation from apparently identical dies.