I remember that when I started opencaching.ro, I chose an ID number (from what was apparently available) and published that choice to OPENCACHING-PL team and on this forum.
Since then the following concept struck me a bit:
Is there an "official" or otherwise unified / organized way of assigning OC node_id numbers?
I mean something similar to internet registered numbers, as held by IANA.
Even if there is none (most likely), I believe there should exist a list of currently assigned numbers published on a webpage (somewhere under http://opencaching.eu/
would be a good choice), along with a set of rules or guidelines on how to register a new number and avoid duplications.