[NASSTY]

Give or take - yes
The way it works is that you have a three year grace period where you are exempt from any ADR changes.
Eg
Start in 2006 finish by 2009 So EUro 4 should be introduced by then but you will be able to use Euro3 engines from either 2006 or 2007.

Start in 2006 finish in 2010 - three years grace is counted back from 2010 to 2007 so the engine is still Euro3. So you could you an engine from either 2006 or 2007 and still be ok.

Start in 2006 finish in 2011. Three years grace is counted back from 2011. So 2008 is when the grace period starts. Euro 4 will be introduced in 2008 so you will need to use a Euro4 engine.

Start in 2006 finish in 2012. Three years grace is counted back from 2012. So 2009 is when the grace period starts. You could use a 2008 or 2009 Euro4 engine.

Do you see the pattern here? I can't think of a better way so say it. Perhaps a table would've been better.
It used to not be so problematic but as I said earlier, Oz is playing catchup to the rest of the world.