^In a letter to Mrs W A Norman in August 1940, Cooper wrote, "I will be 80 years of age on 18th December" - see Document 98 in Attwood and Markus. He died in 1941. On his death certificate, Cooper's date of birth is recorded as 18 December 1861. It is up to the historians to decide which is more accurate, Cooper himself or the author of the death certificate.
^Letter from William Cooper, Secretary, Australian Aborigines’ League, to Isaac Selby, 1 February 1937 qutoted by Attwood, Bain. Thinking Black: William Cooper and the Australian Aborigines' League. Aboriginal Studies Press. Kindle Edition.