You don't need inside info. You only need Wikipedia.
Wikipedia is not always your friend. It is not the definitive source of these things and in the aviation world there are differences from Country to Country and somebody posting information applicable to the US may well be misleading you.
In the UK the list of codes can be found in the United Kingdom Air Pilot although even then you have to be careful because just after the list is another section which tells you that the UK doesn't actually use the ORCAM plan for allocating numbers shown in the list because it is a CCAMS state.
7766 is not a special use code and can be allocated to anybody on the whim of a computer near Brussels