In 2010 the NSW Registry of Births, Deaths and Marriages handed out an amended Birth Certificate to Norrie May-Albie that said, "Sex: not specified". They also created the category "Sex: non-specific".
Non-specific gender was created to cover among others, Intersex people like Mayor X. 50 years ago intersex babies were a 1 in 100,000 birth defect. Now they are 1 in 1000. Mayor X had been born biologically and genitally both and neither male and female. As a young child Mayor X's parents had had surgery performed to create female-type genitals on their baby, who subsequently lived for two decades as a woman. Being a woman did not reflect X's reality, and after two years on male hormones, X settled down to "it's" reality, which was for "it" essentially neuter.
Norrie, on the other hand, identifies as and is biologically 'both male and female". Norrie is a more traditional Male-to-Female Transgender, having hormonal treatments as an adult, surgery to remove "his" penis, but not further surgery to create female genitalia. After years living as a woman, Norrie settled into a hybrid identity that has many feminine traits, but also a lot of male/androgynous traits, a la David Bowie.
After Norris's birth certificate hit the headlines, a higher institution ruled that the Registry of Births Deaths and Marriages had no authority to "create" a third sex. That was appealed, and the Supreme Court overturned the overturning by deciding that "Sex is not binary" and that Birth certificates and other official documents could apply "non-specific/not-specified" as well as "male" and "female" answers to the answer for Sex?.