Originally Posted by
Vuelos
Yes you do seem to be missing the logic.
SDC is only applicable to itineraries that only contain unflown / open US/Can/US Territory coupons.
One can SDC on an international itinerary if there are no further international flights (except for Canada). This is only supposed to be done at the airport. This is a published rule.
Sorry, but I interpreted the first post as applying to itineraries, not individual flights. However, as a statement about individual flights, this would seem to contradict the prohibition on SDCing at the start of an international trip.