canberra
There's plenty of codes in the 77** series
7701-7717 Superdomestic - UK to USA
7720-7727 ORCAM Transit Munich
7730-7757 Superdomestic Shannon Eastbound landing UK
7760-7775 Superdomestic UK to Channel Isles
7776-7777 SSR Monitors
plus pilots are not unknown to get digits mixed up or wrong either ... do it myself when I'm flying as well sometimes.
The conspicuity code of 7000 is only one digit away from that other one.