The limit of indexes varies from state to state...1972 in South Australia, 1985 in Victoria, 1929 Queensland, 1977 New South Wales...I think about 1940 in Western Australia...not sure about Tasmania.
Were your couple resident in Victoria at the time of the accident?...and have you attempted to contact any of the descendants? May be your only hope of finding out any details.
Cheers
Cando