Later amendments can inform the interpretation of an earlier version of the Act, but only where the earlier provision is ambiguous and the amendment wasn’t simply meant to clarify the law and remove doubt2. Even then, you should only use later amendments in limited circumstances – for example, to reject an interpretation of the earlier provision that would make the amendment wholly redundant3.
In this case (at [80-89]), a new provision that expressly says ‘a Minister’ is a ‘public sector agency’ was said to indicate that ministers were previously excluded from the definition of that phrase, as the amendment would otherwise have been unnecessary.
This case is from Episode 18 of interpretationNOW!
3 Grain Elevators Board (1946) 73 CLR 70 (at 86), Episode 16.