A 5+4 formatted ZIP code maps to just a handful of addresses. In cities with larger populations, the +4 could map to a single building, and in more sparely populated place, it might include houses on a handful of roads.

For smaller datasets, ZIP+4 might as well be a unique household identifier. I just checked a 10 million address database and 60% of entries had a unique ZIP+4, so one other bit of PII would be enough to be a 99.99% unique identifier per person.

With a geo-coded ZIP+4 database, you could locate people with a precision that's proportional to the population density of their region.