The 24FEB1924 death date on headstone is wrong. Date-searching on NSW BDM Death Index Nbr: 3981/1925 confirms 25FEB1925, as do several newspaper obituaries, which confirm his 88 years and burial location in Forbes Cemetery. e.g. "Lachlander & Condobolin & Western Districts Recorder" (NSW), Wed 4 Mar 1925, Page 4.
trove.nla.gov.au/newspaper/article/213514383
As husband's & wife's graves stylistically match, it could be that William's grave was refurbished at the death of his wife in 1939; misrememberance of the death date 14 years later could possibly be a reason for the error.