CPL exams expire after 2 years I’m not aware of any expiry around PPL or RPL.
Read up on Part 91. It only updated last December and many places are still trying to get up to speed.
If you don’t re brief you will get caught out in CPL theory if some of the basics have drifted away.
https://www.casa.gov.au/sites/defaul...ve-version.pdf