Yes. Ultimately, "are these the same" and "are these different" are philosophical questions. Or to be more precise, teleological questions. Because those quest

Yes. Ultimately, "are these the same" and "are these different" are philosophical questions. Or to be more precise, teleological questions. Because those questions have no meaning except with an "for our purposes here" added. And it's up to us to decide what we care about, if anything. If we care about what other people want with the data though, or suspect that our own wants might not be set in stone, then we should also care to model identity independently in the system (that is, use surrogate keys).