> It was never part of the UN and its membership was explicitly denied.

Solely due to a soviet veto. Most countries recognized it anyway.

> Most countries recognized it anyway.

No - most Asian nations did not recognize the South Vietnam govt propped up by Western powers. India for example supported Vietnamese independence from the French and recognized the PRG - Provisional Revolutionary Government which was the resistance movement in South Vietnam.

At any rate, even the US vetoed Vietnamese membership to the UN in 1975 - after losing the War.

> No - most Asian nations did not recognize the South Vietnam govt

I would not say "most". Thailand, Laos, SK, Philippines, Singapore did.

>US vetoed Vietnamese membership to the UN in 1975 - after losing the War.

Because the war was still ongoing, between North and South at that time. They merged in 1976 and US voted in favor of membership in 1977.

> US voted in favor of membership in 1977.

Only because Jimmy Carter got elected in 1976 on the basis of a campaign pledge to forgive all draft evaders and beat Ford. Until he was elected, Vietnam was three times blocked from admission by United States vetoes in the Security Council.