Merchant-defined zones are resolved first match, so an order to a country nobody listed would otherwise have no shipping rate at all. Rather than pricing it at zero, which quietly flatters the margin, it falls to the catch-all and the country is flagged so the gap can be closed deliberately.
Assigning a country to a zone removes it from the zone it was in, because a destination can only be in one zone at a time. That mutual exclusivity is what keeps the resolution unambiguous and the rate card readable.
The flag is the part worth acting on. A country repeatedly resolving to the catch-all is either a market worth pricing properly or one worth not shipping to, and both decisions are better made from data than from a shipping bill.
The catch-all still needs a price of its own. A parcel to any zone that no active rate card prices is flagged as well, rather than shipped for nothing on paper, so a zone added and never priced cannot quietly make a market look cheap.
