The Vietnamese are still making excuses to try and squirm their way out of Premier Pham Van Dong's 1958 signed diplomatic document to China (see
VietNamNet - Diplomatic Note 1958 with Vietnam). The arguments presented are not very convincing. Fundamentally, North Vietnam was succeeded by unified Vietnam. Unified Vietnam, as the successor state, CANNOT disavow prior diplomatic documents and obligations of North Vietnam.
I have already mentioned that Premier Pham Van Dong served as Premier of North Vietnam for 20 years and then Premier of unified Vietnam for another 10 years. The continuity in government from North Vietnam to unified Vietnam is clear. Similarly, the legal effect of the diplomatic documents of North Vietnam is continuous as well.
The national flags of North Vietnam and unified Vietnam exhibit the same continuity in government from North Vietnam to unified Vietnam. The government of unified Vietnam was exactly the same as North Vietnam, except it covered a larger territory. Therefore, we can only conclude the successor state (i.e. unified Vietnam) cannot disavow the Diplomatic Document of 1958, which China had relied upon for 53 years in her foreign relations.
Under the legal principle of "detrimental reliance," Vietnam must be estopped from denying the factual admissions in the 1958 diplomatic document by Premier Pham Van Dong.
Detrimental reliance legal definition of Detrimental reliance. Detrimental reliance synonyms by the Free Online Law Dictionary.
"
A legal principle that bars a party [Vietnam] from denying [1958 Premier Pham Van Dong's diplomatic document] or alleging a certain fact owing to that party's previous conduct [acquiescence for 53 years], allegation, or denial."
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The flags of North Vietnam and unified Vietnam are one and the same. The Vietnamese government was continuous.
"The flag of Vietnam, also known as the 'red flag with yellow star', was adopted as the flag of the Vietminh (Communist army) in 1941.
It was adopted by the Democratic Republic of Vietnam (the future North Vietnam) in 1945, and by the Socialist Republic of Vietnam (united Vietnam) on July 2, 1976, following the end of the Vietnam War"
Source: Wikipedia