some sources say it is from 1947 to 1955 while other 1947 to 1962... which opinion is correct?

Era of tight bipolarity was from 1947_1953; year of 1953 brought an end to it as change of leadership occurred in both States.
In a tight bipolar system, international organizations either do not develop or are ineffective. In a looser system, international organizations may develop primarily to mediate between the two blocs

1947-1955 Not 53

It is correct that the government changed in both the superpowers but it didn't diminish the confrontation between them. In-fact, Eisenhower, who was elected in 1953, aimed a more aggressive policy towards the Soviet Union and blamed Truman of adopting soft policies against the Soviets.

Nikitiv's, elected in 1953 after Stalin's death, internal policy provided some relief to the Soviet Public; however, his external policies regarding Soviet satellites and Western Capitalism were no less aggressive than Stalin. Warsaw Pact-1955, Poland Crisis and Military invasion of Hungary was carried out under Nikitiv.

Geneva Conference of 1955 promoted a sense of mutual co-existence. Eisenhower open skies policy and sharing of military blue prints between both states put an end to tight bi-polarity. Although U2 crisis and arms race began later, but Geneva conference of 1955 demonstrated the opposite side of both the countries showing that both can mutually co-exist. So political scientists mark 1955 as the end of TIGHT bipolarity.

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