AH'
This explains it.
Here is a service history for the man and he was known by all the given names we are exploring

Name -GRUNDY, FREDERICK ALLAN DOUGLAS
Service Australian- Army
Service Numbe-r T21524
Date of Birth -29 May 1907
Place of Birth -COLEBROOK, TAS
Date of Enlistment- 21 Jan 1942
Locality on Enlistment- WEEGENA, TAS
Place of Enlistment -DELORAINE, TAS
Next of Kin GRUNDY,- BERYL
Date of Discharge -24 May 1944
Rank Private
Posting at Discharge 6 GARRISON BATTALION
Sue