That worked, all 12 are up. I did hit the device_exists thing straight away because I’d erased flash on node 3 while debugging, it had already registered as aq-3c84a1. Deleted that device in the console and it provisioned again fine. Activated them all from quarantine this morning. Also had to escape the quotes properly, my first version sent broken JSON and just got nothing back.
Timestamps in UTC or it didn't happen.