We have a large number of circles and frequently see the repeated role issue, particularly for internally focused team specialists (ERP Expert, Lean Practices Champion, etc.). It makes our records look a little sloppy, but I think the alternative--a centralized repository--may discourage evolution of the roles within each circle to help the circle pursue its purpose and accountabilities. Provided that your circles are engaging in regular governance rhythms and your people are actively reflecting on their roles and evolving them through governance, I'd be inclined to let each circle draw up exactly what it needs.
I'd see an exception in the event that there is an organizational need for standardization (i.e. each circle needs to have someone monitoring for unsafe working conditions and we need a standardized definition of what that means).