On 18 June 2008, the ATO issued an Addendum to GSTR 2002/3 (Goods and services tax: prizes). The Addendum amends GSTR 2002/3 to clarify the GST treatment, under the GST global accounting system for gambling supplies, of monetary prizes that have been declared by the gambling supply provider, but not paid. It also provides guidance on the GST treatment of cancelled refundable bets, and unclaimed amounts. It has been amended in light of the decision in TAB v FCT  NSWSC 552; 2005 ATC 4512, 59 ATR 430.
For a copy of GSTR 2002/3A2, go here