http://asic.gov.au/for-business/running-a-company/shares/cancellation-of-shares/
It says "if" they cancel the shares the company has to notify ASIC.
This link talks about share buy backs but does not mention that the company has to cancel them
http://asic.gov.au/for-business/running-a-company/shares/share-buy-backs/
Another link below talks able the shares bought back can be resold on market at a later time
http://www.investopedia.com/ask/answers/05/retiredstock.asp
So it would appear that BRS buyback of shares do not necessarily have to be cancelled.