"country": what to for "strange" locations?

Hello...

I know there's "EU" for europe, but what to use for:
    - anycast services without any specific location
    - blackholes
    - ...

For example, 193.0.14.0/23** (k.root-servers.net) uses "country: NL". 
Documentation says: "There are no rules defined for this attribute."

Is there a best practice? If not, is there a chance to get "ZZ" approved 
for "unspecified" as ISO 3166-1 specifies "ZZ" (and some more) for 
"/User-assigned code elements"...

Best regards,

    Christian


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