if the bearings are not dull and I don't see any signs of rust or pitting, even with a visible ring where the bearings run i don't hesitate to reinstall. On old cones like that which I suspect are fairly soft compared to say campy records, I would guess that that mark would appear in a new cone within a few months or even weeks of riding. That is how it is with the cheep suzue cones I often use to rebuild sunshine and suzue hubs. they are a dark colour, almost black, when new and the first time you open them up after installing them and a few rides that silver rings has appeared. I will agreee with the "think of it as broken in" school of thought.