Objective, measurable, and not yet
Campbell has a phrase for the only kind of verification he accepts. Tasting the pudding means testing the value of an experience, a truth or a piece of knowledge by the objective, measurable results it produces. If what you take for truth cannot honestly produce those, it comes out of the truth bin and goes back into the interesting-possibilities bin.
Applied to this practice, the instruction has a date on it. Do not begin to judge how well or poorly your meditation is working, he writes, until you have run a productive process twice daily for at least three to six months. Then taste the pudding. Then keep tasting it at three-month intervals.
The test itself is the striking part, because it is not introspective at all. After six months, ask people close to you whether they notice a change in your approach to life. Not whether your sits feel deeper. Whether other people can tell.
That follows from everything in Stage 3. If understanding stays intellectual it is not understanding yet; real assimilation modifies your intent and shows up as personal change. So the evidence is behavioural and it is held by other people, which conveniently makes it much harder to fake.
Which is also why this app has never scored a session. There is no honest metric available before three months, and the one that arrives afterwards is a conversation rather than a number.