It's not a grace year, Arwen mentions it above as part of the regulations:-
"must have been a permanent resident for the 12 months immediately before making an application and not have been absent from Australia for more than one year in total, during the four year period, including no more than 90 days in the 12 months before applying."
Dunnyboy's legal entry date was Nov 2012 and the four years start ticking from then but he has effectively have to have spend 3 years out of any 4 in the country, so as long as he doesn't leave his 4 years (3 in the country) finishes in Nov 2019.
The change now means you have to have been a PR for all four years now, rather than just the last one.
Edit: Ali beat me to it.