My current WAG is that "the Circle" (aka "Black Council," treating them as the same for the nonce) doesn't really exist, as such: that it's mostly-disconnected individuals, not cooperating or coordinating with one another.
The unity-of-purpose (and appearance of coordinated action) comes from the united purpose of the Outsiders (who are canonically (i.e. according to unreliable-narrator Harry Dresden (upon which my whole WAG hangs)) utterly unified), not from coordination by the people allegedly on the Circle/BC. Some of the Outsiders' servants are very-powerful wizards and Vamp nobles and such, who create Hexenwulf belts for Law-Enforcement, and give heart-ripper spells to small-time wizards (or surface the Word of Kemmler).
But the fact that all these plots are coming to fruition where Harry gets to enjoy the harvest isn't because the people enacting those plots from behind the scenes are cooperating with one another to bring all these things to a crescendo. It's because the Outsiders are doing so. Like wrenches and screwdrivers in a toolbox aren't "cooperating" with one another, even when they work on the same project.
Realistically -- which the Dresden Files admittedly are not! -- I don't think a diverse group could have actively worked together for so long, interacting with cats-paws (of dubious and varying loyalty) and the rest of the supernatural community, and still maintained secrecy.
It's more like small "cells" of operatives than a "circle" ... each top agent within the world (and/or the Nevernever) runs their own cell of agents. These top agents may, occasionally, interact or cooperate -- when so directed by the Outsiders -- but they don't form a "Circle" or "Council" that is self-organized as a group.
That said, there's no reason my own view is incompatible with the OP: when the outsiders get a highly-functional group of top-tier servants, they may operate those same individuals for decades on end, going back to the same toolbox because something there always works. But then they lose one because a Starborn tool takes out the Red Court (or some such nonsense), and the Outsiders' toolbox no longer can be relied upon to solve the problem; and at that power level, there probably aren't 1:1 replacements readily available...
So -- sometimes -- a whole new (or mostly-new) toolbox.