There were thousands of runic circles, and not all were functioning; actually, none were functioning. But Damian still etched them on the surface of the metals by somehow joining the pathways and at least having one tiny functioning spell inside.
Usually, a failed runic spell would never be inscribed in the metal. But if there was one full runic spell section with complete paths and full circles inside the mess of a giant, complicated runic circle, it would work. The faulty runic pathways won't work into anything useful, but they will still be inscribed in the metal, and the surface will show the full, complicated runic circle.
Imagine a large, complicated electrical circuit board with wires, switches, capacitors, and many devices connected. Most of those devices are broken or disconnected internally, so electricity cannot complete a loop through them.
