Great idea Mum Mum re: contacting the local family history group! Do hope you have some luck with that avenue.
In the meantime: some notes about Joseph John HOLMES that I've found --
(pieces to the puzzle in case)
Not sure whether you have seen the private Ancestry 'tree'/notes that come up in a search there for "Joseph John Holmes d. 1963" the one with the title that says "Joseph John Holmes Clark // 'who is father is'"? Maybe someone to contact if you've not seen it.
Checked the NAA website and it seems Joseph also served in WW1, you can see his service record on the NAA site
http://www.naa.gov.au/According to that, he was 39yrs + 1 month on 1st Feb 1916.;
that gives his birthdate as roughly 1st Jan 1877, which supports the earlier 24th Dec 1876 birthdate.
Interestingly, he gives next of kin there as his mother "Jane HOLMES, Bethangra VIC" - in 1915.
Wonder why not Jane CLARKE...?
(More about him also by the way on the AWM website:
http://www.awm.gov.au/research/people/all/?Name=joseph+john+holmes&ServiceNumber=&Unit=&Conflict=All+conflicts)
However, according to the NSW BDM index (deaths):
10552/1963 HOLMES JOSEPH JOHN WILLIAM JAMES JANE ELIZABETH TUMUT,
so this death cert says his father was William, who died 1yr+2mths before 24th Dec 1876.
Then, I did a Google search for "Holmes, Joseph John", and his record came up here:
http://www.monaropioneers.com/Descendant-reports/AIF%20Volunteers.pdf... giving his birth details as "1873, Gundagai NSW"! Also says there he died April 15 1963, buried in Batlow cemetery.