I've found the GWGC people to be a bit obstinate, to be honest. I have a relative whose mother died during a surgical operation shortly after he fell on the battlefield; it was said that the father then died of grief at losing wife and son in such quick succession. I have newspaper announcements to show the dates of death, i.e. that they were alive when he was killed, but the CWGC is not prepared to change the wording "the late" submitted by their daughter (the soldier's sister) after the war.
Sooner or later, we're all "the late"! I maintain that it's irrelevant that the parents were dead by 1919.