Oates and Oates (1970:209) say that this is a group of tribes including Bujindji Y87, Njunggal Y90 and Waldja Y98, while Roth (1898) says that 'Wool-boorjoor-boor natives' (Y148) speak a language called 'Ko-ko-min-ni' Y94.
Based on the available information, Wulbudjibur is unlikely to be a language name.
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).