You are right. You can do that. There is no rule that you have to stay 2 years continuously. It's just that whenever you stay in Aus (continuously or by part), you should stay in Vic for first 2 years of your stay in Aus (so you can stay in batches, let say initially for 6 months, then in 2018 you come back and stay 1 year, and then 2020 you finish last 6 months of the the 2 years quota).
it's just that you have to give an entry, even if for 1 day, to Aus by July deadline.
And another thing is though your visa is valid forever, your entry permit is valid for 5 years. That means if you can't obtain a passport by that time, you can not re-enter Aus after 5 years with this visa (but if you are in Aus at that time, you can stay without an issue) unless you get an extension (in the form or resident return visa). So you should plan accordingly.