A death certificate for 1961 should have a box asking if Veteran. I have seen Yes, No, or Branch typed in.
He filed WWI Card in Onocee County but he was not in their list of the Soldiers Discharges Index 1914 to 2001. http://gaoconee.eppygen.org/Mil_Soldier_Discharge.htm
To look at other counties for sources of records:http://www.thegaproject.org/
Try local newspapers where lived 1918 to 1919 as they had lists of men that enlisted and returned home.
You also might try the GA National Guard, could be he enlisted with them and the war ended before unit was "Federalized" and never left the states. If the National Guard Unit was not Federalized then there will be no records at the NARA only at the State Archives or GA Guard records storage. Also 1930 does ask if serves in U.S. Armed or Naval Forces and NG was not considered "U.S." but a State Militia, unless "Federalized"
By 1940 NG service could then have been considered "United States". So box 39 has "yes". What is in box 41? Should be an W or S or SW or R or Ot.
Great WWI Site:http://freepages.military.rootsweb.ancestry.com/~worldwarone...
The 1973 Fire at the NARA did destroy about 80% of Army/Army Air Corp/Air Force records from Spanish American War to early 1960's. Navy, Marine and Coast Guard were not affected as they were not stored there then.