Hey guys,
After processing three times 489 visa's for different people in my family, my experience says:
We never got notification about CO assignment. In all three cases (1st 6 years ago, 2nd 4 years ago and 3rd recently) CO never contacted us and we got visa grant directly. We always supplied all the documents while lodging even optional one's. And we didn't engage any agent/consultant either.
For all three cases, even in different years, we got grant between 3 and 3.5 months from date of visa application submission.