My grandfsther was KIA in 1916, when my father was aged 2.
The Lives of the First World War had his date of death, from his medal index card at the IWM.
I submitted "evidence" linking to his entry on the CWGC records, as well as uploading scans of a newspaper report of his death and a copy of his birth certificate re. his date of birth.
All this was added to the website, although I can't remember how long it took, but I think the info you submitted will eventually be added.
One thing I would like to know is whether the evidence I submitted re his date of birth will find its way to the CWCG records, as they do not have that recorded and consequently it is not shown on his gravestone in France. If anybody knows the answer to that I would be grateful to hear it.