I have read the Its an Honour site quite thoroughly and I may just be stupid but I do not see how there could ever be a prescription along the lines of You must always include all postnominal letters to which you are entitled after your name which is what I was trying to say when I said that it is up to the individuals discretion For example a close friend of mine is entitled to use the DSO postnominals after his name but he does not always do so as he feels it is not always appropriate Further he has many ribbons he is entitled to wear but in situations that call for ribbons he does not always wear all of them You did not point me to any rule stating which may be worn only a list of those which have a particular precedence and vague rules for foreign awards Thus as there is no rule saying you must always use all your entitled postnominals the fact that General Cosgrove did not use CNZM is not evidence that he could not  Again I read the references but did not see any rule saying that postnominal letters cannot be used unless authorised by the GG It indicates that there are awards Australians may not accept and may not wear but does not say that it is an exhaustive list CNZM is obviously an award Australians may accept as several have It also obviously does not have a specific precedence but I have not been able to find any information indicating that Australians may not use its postnominal letters