The Returned and Services Association says it still has faith in security measures at Waiouru Army Museum, despite the loss of more medals.
Two sets of World War I medals gifted to the Waiouru Army Museum in 1979 and 1984 were found to be missing in November 2009, the army has confirmed.
The loss follows the theft of rifles and other property by a curator last year and the burglary of 96 medals, including nine Victoria Crosses, in 2007.
Association president Robin Klitscher says the loss of medals is regrettable. "They have monetary value, in many cases, but the emotional and social value to the families is immeasurable."
However, Mr Klitscher acknowledges the museum is making strides towards improving security.
He suggests the latest loss may be historical and uncovered only because of a continuing stocktake of property.
Army spokesperson Kristian Dunne says that although the medals were discovered missing last year following checks, it is not possible to say when they disappeared.
Lawyer Chris Comeskey, who helped broker the return of medals stolen in 2007, says the army could have made public the latest loss when it was discovered.
If there had been publicity at the time, he says, whoever has the medals would have been made to think about the public backlash.
A war historian says the missing medals could be worth tens of thousands of dollars.
Glyn Harper a professor of war studies at Massey University, says gallantry awards would enhance the value of the medals considerably
Dr Harper says a set of First World War campaign medals in good condition can fetch more than $3000, while gallantry awards will bring tens of thousands of dollars more.