A plausible answer is an observation, not proof that the system works. You need examples with criteria you can check, traces that show how answers were produced, and a release decision that was not tuned to the test answers. This holds for document extraction and for agents that change files or call services.
An application with a good interface and no labelled examples is hard to improve, because you cannot tell whether a change helped. Add a hundred hand-labelled traces, a written list of failure modes and a judge checked against your own labels, and it becomes a different thing. A trace is the saved record of one request: input, intermediate steps and output. A judge is a model prompted to grade another model's answers against criteria you wrote. These records help you explain failures and compare changes, but they do not replace a domain expert or application-enforced permissions.