score:3
From the Australian Customs site:
We no longer stamp Australian passports as a matter of course but should you require evidence of travel you may ask one of our officers to do so.
So no need to be concerned, it won't be a problem in the future. They do record it electronically.
Upvote:1
Some countries have a general presumption that you departed before you visa expires, so it's not a problem unless you are found in the country after the expiration date. Assuming you departed by a commercial carrier, immigration gets passenger lists from the airline/ cruise company and can match up arrivals with departures that way.
If, for some reason, it does become an issue you just have to provide some evidence that you were somewhere else - work records, boarding pass, entry stamp of another country etc.