The bullets on the KEYone are plated plastic with adhesive to hold them in the recesses. The fact that they're recessed doesn't mean they're part of the back plate. It's far less expensive in manufacturing to rubber coat the back plate and adhere the bullets later than to create a mask during the rubber application process. The rubber is sprayed on like paint and cured under heat to vulcanize it to the substrate.



If it were masked off as you're suggesting then it would create multiple edges where the coating could start peeling. Instead, the rubber can be applied as one layer and the bullets sit down inside. The recess helps mechanically retain them.



It's easy to prove. Take an X-Acto knife to one of your bullets and pry it up.



From the BB10 generation and beyond, the Q10 and Z30 had aluminum bullets that were molded as part of the back covers. Most other models had applied bullets.