Christine Caldwell Ames distinguishes between the idea of “the” Inquisition and the historical reality.
The medieval inquisition was really in no way an institution. And historians now do like to use the plural, and say very insistently inquisitions, to designate that these were individual trials that could happen very successfully, or also could again be stymied in different ways.
Then, only later in the Middle Ages do we see the evolution of a kind of institution, that is, different offices, different inquisitors, who are communicating with each other, who are leaving records that future inquisitors will leave. And we really don’t see any kind of very sophisticated machinery that has a large apparatus, say, of supervision and punishment until the later Spanish Inquisition and Roman Inquisition.