Derived postcode places are what a national address register contributes to a country's postcode directory as it is compiled: for every postcode the register's buildings carry, the towns those buildings are written with and the mean of their positions, added to the directory beside what the directory already lists.
What Spaw answers
Ten registers declare it — Switzerland, Austria, Czechia, Norway, the three Belgian regions, Luxembourg, Australia and Latvia — and after each compiles, codes the directory lacks are inserted under the register's own -postcodes dataset, and codes it holds gain the register's places after their own and a centroid only where they had none. locality_matches_postcode then knows every town a register writes under a code, not only the operator's default one, and postcode_status: live answers for codes the postal-code dump never carried. The weekly places sync re-applies it after the dump's own replace.
What it does not mean
It does not make a directory complete, and it does not replace one. A register of buildings never lists box-only and large-recipient codes — Swiss and Austrian Postfach codes, Australian GPO boxes, Czech special codes — so replacing the directory would have turned real box addresses into postcode_not_found; coverage moves to complete only when the operator's published total is configured and the union reaches it, and no country's total is configured yet. The United States gets its extra places from a different source, the Census Bureau's ZCTA-to-place file, and stays unscored on a town mismatch because that file lists places whose land a ZIP touches, not the names the postal service accepts.