The basic problem is one of tracking (or not tracking) copies of data. Your information at Facebook is stored primarily on several storage systems, but extra co

The basic problem is one of tracking (or not tracking) copies of data. Your information at Facebook is stored primarily on several storage systems, but extra copies might exist in backups, data-analysis pipelines, logging systems, etc. At the time I left (two years ago), there was a cutely-named project well under way to ensure deletion of those primary copies and (IIRC) backups. Fragments still in data-analysis systems might still exist, but they're also less personally identifying. I don't recall the state of anonymization and provenance tracking that would allow even these remnants to be found and purged for certain. So we're basically talking about two different questions. (1) Is it possible to be sure that the primary copies and backups are gone, so that finding anything that's left would require some very specialized knowledge and/or an infeasibly massive scan? I believe the answer to this is probably yes at this point. (2) Is it possible to be sure that absolutely every last vestige of the person's time on Facebook is gone? I believe the answer to this is still probably no, and likely to remain so for some time. At the very last, some artifacts will remain in those opaque AI models. I suspect the same two answers exist at many companies. What is HN's data retention policy? Oh, oops, none of my data would be deleted if I left. I suspect that Google and/or Apple, maybe Microsoft as well, are a lot closer to "yes" on that second question, but even then I suspect gaps appear from time to time. I say this not to condemn or defend anyone, and I know companies under stricter regulatory regimes can give more definite answers. It's just the state of the art at Big Tech companies as I understand it.