There is nothing new in the regulations have been around for quite a long time - in fact about as long as tow bars have had to have compliance plates so about 10 years or so. Prior to that I think you are on your own and almost anything can be fitted - the rego rules on removing rops for Perenties probably doesn't have a leg to stand on if someone took up the legal cause due to their age, exactly the same if a 5 poster bar was fitted would not be illegal as the age of the vehicle predates the more modern rules.
So if the compliance plate/sticker says it is complied for your model Territory then you will be fine.
As you might be aware I have a Range Rover Sport - basically the same a Disco 3 and the Disco 3 bull bar fits straight on BUT it cannot be legally fitted as the compliance plate names the D3 not a RRS so I cannot fit one to my car.
Garry