Australian States NSW 1871 8d Yellow on Cover Sydney to Germany

1881 (24 Jun) envelope to Germany bearing 1871 8d Yellow Perf 13 tied by Sydney 'N.S.W.' in concentric ovals duplex, and endorsed 'Via Naples per John Elder'. The correct rate to Germany at this time was 9d, and the boxed 'INSUFFICIENTLY/PAID' was applied, also the rare diamond 'GB/1F66c' Anglo-French accountancy mark. The latter would seem to be an error, as this cover was not routed through France. An unusual usage