Identifying each egg should help to control egg substitution but there are a couple of problems. Firstly, backyarders with 50 hens or less are exempt - so that that means Victorian consumers are being put at risk by buying something like a million eggs a year which cannot be traced. It is unfair to impose regulations on just some sellers. The same standards should be applied to anyone selling eggs (give them away by all means but all egg sellers should have to meet the same regulations).
Secondly, it seems that eggs can be stamped on the grading floor. That defeats the object of stamping to identify the farm on which the eggs are laid. Staff at the grading floor can use any stamp they like so unless the eggs are stamped on farm before they are sent to a grading floor, there can be no guarantee that the eggs are from the farm identified by the code.
Here's a link to an article in Tassie about the nonsense which has been generated there by people who don't care about food safety: http://www.themercury.com.au/lifestyle/our-storm-in-an-egg-cup/story-fnj64o9j-1226754065881