> the result of which would be just that X hashes marched but not which X
That means you can't prove an incriminating file was not deleted even if you're the victim of a false positive. So they will suspect you and put you through the whole police investigation routine.
Not necessarily it just means that you don’t know/prove until a certain threshold is reached, in guessing above a specific one that hashes and the photo is then uploaded to Apple for verification and preservation.
