According to Wikipedia, there was a missed opportunity to discover the Van Allen radiation belts during Sputnik 2:
In Australia, Professor Harry Messel intercepted the signals. Other stations in Australia and South America had also been in range and intercepted the signals. However, the Soviets would not release the code that would allow the stations in Australia and South America to read the signals, and without the code, the stations would not cooperate and send the data to the Soviets.
The disagreement cost the Soviets the opportunity to claim one of the most significant findings of the space race at that time, and only after the launch (1 February 1958) of the U.S. satellite Explorer 1 did James Van Allen demonstrate the existence of the radiation belts. In 1958, with Sputnik 3, they began to cooperate, and they confirmed the findings of the U.S. satellites Explorer 1, 3, and 4.
After the Soviets began cooperating with western scientists, was the Van Allen data of Sputnik 2 collected in Australia ever analyzed? Does it show the existence of the belts?