Further to the occasional posts on the 'South Vietnam' clasp to the 1962 GSM awarded only to members of the Australian Army Training Team, I have a suspicion that the recipients were later offered the opportunity to 'convert' this to the Vietnam Medal (VM - awarded for operational service in South Vietnam between 1964 and 1973).
Nugget 90 It seems others - in particular RAAF - were awarded the clasp, but they subsequently had it removed
and replaced with the Vietnam Medal, leaving only AATTV as recipients.
Wiki (usual caveats!) has it thus:
South Vietnam
This clasp was instituted by Royal approval on the 16 December 1965 for "members of our Australian Armed Forces who qualify by participation in operations in defence of the Republic of Vietnam as from 24 December 1962, and to a date to be determined,..." Between 1963 and 1965, at least 68 members of the Australian Army Training Team Vietnam (AATTV) and 232 members of the RAAF Transport Flight Vietnam qualified for the clasp. However, a decision of 1966 relating to the institution and award of the Vietnam Medal led to the stripping of the award from the RAAF personnel. A Royal Warrant dated 8 June 1968 retrospectively changed the qualifying periods to:
Between 24 December 1962 and 29 May 1964,
30 days' service in ships operating in inland waters or off the Vietnamese coast.
1 day in the service of a land unit.
1 operational sortie.
30 days' service on an official visit.
For service after 29 May 1964, personnel were awarded the Vietnam Medal. Thus, only 68 clasps were issued, and all 68 went to AATTV members.