Do either of you have the 1939 Register access from FindMyPast? I wonder if William and Mary Griffiths were still living in Ponkey or vicinity.
Just dabbling, I found an Oswald Griffiths who played football for union and league teams in the 1930's. I can't find much on-line, but I wondered if he might be the Oswald from this family.
Oswald seems to have been a forename in use in the area around Ruabon in the 19th Century. I thought it might be uncommon.
The search continues!
