@CDonohoe So it turns out that there was a miscommunication with the manufacturer. This issue has been sorted now. If you power cycle your gateways, they will connect to the EU router.
Also, curl -k -i -X POST --data '{ "router": "58-A0-CB-FF-FE-80-1D-F4" }' https://mh.sm.tc:7007/update-info
now yields a 401 Unauthorized, Wrong Token, where before provisioning that threw 404 Not Found, Not Provisioned. So, that really seems like a good way to check.
Still not clear to me if @CDonohoe also registered the TTIG in TTN Console. https://www.thethingsnetwork.org/gateway-data/gateway/eui-58a0cbfffe801df4 no longer is empty, but shows no owner. And https://www.thethingsnetwork.org/gateway-data/user/CDonohoe does not show that gateway either. Could also be related to privacy settings I guess, though the first was empty before the fix, despite it being registered in TTN Console.
Good news, my gateway is up and running…
Thanks everyone for your help. My faith has been restored.
Caoilte