Speaker numbers were measured differently across the censuses and various other sources listed in AUSTLANG. You are encouraged to refer to the sources.
Speaker numbers for ‘NILS 2004’ and ‘2005 estimate’ come from 'Table F.3: Numbers of speakers of Australian Indigenous languages (various surveys)' in 'Appendix F NILS endangerment and absolute number results' in McConvell, Marmion and McNicol 2005, pages 198-230 (PDF, 2.5MB).
Sharpe, Margaret. 2005. Grammar and texts of the Yugambeh-Bundjalung dialect chain in Eastern Australia. Munich: Lincom.
Allan, John and Lane, John. 2001. The language of the Wangerriburra and neighbouring groups in the Yugambeh region. Kombumerri Aboriginal Corporation for Culture.