From the CASA web site.
https://www.casa.gov.au/standard-pag...tions-answered
The expiry dates for ASICs are based on the date of the criminal history record and is always the last day of the month. The date of expiry of an ASIC must not be longer than two years from the time the security checks are completed. This means that if your security check was completed on 11 May 2009, your ASIC would have an expiry date of 30 April 2011.
ASICs are issued following the background security check and assessment. In some cases the assessment process involves further investigations before the card can be issued. In this instance the validity period will be reduced depending on the outcome of the assessment of the application, and the eligibility period will usually be not more than one year.