A small point:
Parliament has the power to enact legislation within a sovereign country.
Typically it will do this via Acts, which themselves may give rise to regulations, which can define rules, and may make reference to various other national and international documentation.
It is not uncommon to say in enacting legislation that where there is conflict between another document and that Act, that the Act is the authoritative document. Likewise with regulations.
Now I've no time left to devote to this today, and have conducted nil research, but I suspect you'd find that if any ASTM documentation is referred to in any Australian legislation it will be in an advisory role, and in any case cannot (or at least should not) trump the right of Parliament to enact legislation within Australia. Thus CAO 20.16.3 probably remains the authoritative source on this matter.
Quite apart from that one would need to see the detail of any ASTM documentation to determine exactly what it says on this, and whether it is relevant to matter at hand.