I agree we are not using the same definition of data discovery. In my use case, you know a priori which user provided the data, you just need to plumb the information through to all downstream systems. This seems sufficient for GDPR as I understand it. I had not read your entire comment and did not realize you were promoting a system to try to do something like this automatically. I did not realize the initial question was rhetorical.

FWIW I would be worried about relying on such a system! But based on the description it seems helpful. What does it do about derivative data that doesn't directly contain any PII?