Less than 100 votes triggers a recount.

They conduct an informal ballot paper study following every event. The latest published ones I could find were from 2016:
www.aec.gov.au/about_aec/re...

Well, to be fair...

The count of ordinary votes at polling places has finished. They are still counting some declaration votes.

This was the link they used - they didn't include this bit in their screenshot either.
www.theaustraliatoday.com.au/recount-dram...

They do? The screenshot above is not from the AEC

It's enforced regularly. There are some people who fly under the radar but many, many people are enrolled without filling out a form. Trust me, after each election the AEC's phones are flooded with people who got failure the vote forms even though they didn't realise they were on the roll