Scirocco Central

Rear brake discs usage/ wear.
Today, I noticed the front discs are shiny & used across the full diameter, without any rusted outer circumferences.
But the rear discs have an outer circumference that appears not to have been in contact, ever, with the pad.
I appreciate the braking bias for the front, but Is this normal?

Yes, perfectly normal, with relatively light, ie non-urban driving. With that level of rust, no concern, but check the rear face as well. Your MOT tester and/or vehicle technician may note it as an advisory