The "opposite" of the Christmas Island situation occured a few years ago (around 1996) for the (British) Channel Islands, and I had a few discussions with IANA/Jon Postel about these at the time - now .gg and .je.
These strongly indicate to me that ICANN do not now have, and never had, a solid rule on what consitiutes a valid geographical TLD, which is what allows the .cx confusion to exist in the first place.
The bottom line then was that a scheme had been chosen for geographical TLDs, and that scheme was the ISO 3166 list of two-letter country codes. Except for the exceptions. And those exceptions followed no rule.
Now, I found that an interesting attitude. The ISO table had allocated an entry for
which is politically very different from "The United Kingdom of Great Britain and Northern Ireland". The net community, before adopting ISO 3166, had used .uk for Britain in the same way that the Australians had used .oz (i.e. by private concensus. Actually, as far as I can find, .oz was created by the University of Sydney. I'm hunting down more info. See Roger Clarke's Brief History of the Internet in Australia).
However, where the Australians eventually reallocated all their names from .au, no such measure was required for .uk - in fact, .gb was listed as "depreciated". In the case of the Channel Islands, although self-governed (and therefore not part of the "UK"), they still have the Queen as the head of government, and also firmly belong to the entity "Great Britain". We wanted to be able to issue domain names for Channel Island entities outside of .uk, and thought that .gb would be the ideal place for them. Jon would not allow a registry for .gb to be created. This was probably due to the common mis-apprehension that because the full name for the UK includes the phrase "Great Britain", the UK must be a superset of GB, where in fact the situation is the reverse.
The other option was that each governed area should have it's own TLD. To this end, it was suggested that the Islands' should apply for their own ISO 3166 code. This would be an extremely slow process! I believe that the ISO 3166 committee only meets once every 4 years. A variation on this view was what eventually persuaded Jon Postel to ratify .gg and .je, which (IIRC) are international postal codes.
So now the exceptions to the geographical TLDs included .gg and .je (and .im for the Isle of Man, in a similar political situation). I can't currently find the "definition" of geographical TLDs, but I suspect that ICANN have done away with any formulaic definition, because of the number of exceptions they have allowed.
So, to recap - geographical TLDs do not follow a fixed allocation rule. Therefore arguments based on the supposed "fixed and valid" status of a TLD based on it's existance are, unfortunately, unstable.
Quick wafting zephyrs vex bold Jim