@Toretti said:
Who, in the end, decides authoritatively what is and what is not common property or whether common infrastructure is the responsibility of the owners corporation?
The second part of your question is answered by the Strata Schemes Management Act, the Strata Schemes Development Act and the Strata Schemes Regulations – which basically say the Owners Corporation must maintain and repair common property and “any personal property vested in the owners corporation”.
Your strata plan lays out what is and isn’t common property but in the event of a major dispute, I would imagine a case run at either the Supreme Court or even the Land and Evironment Court would give you a definitive answer (at considerable expense)