There are some historical events where it may be impossible for ordinary people to learn the truth. For example, there are situations where more than one nation state has a good reason to circulate a false history — complete with credible-seeming historical documents.
One such case may be the 1979 Vela incident, in which an American satellite may have detected a clandestine nuclear test in the Indian Ocean. Some analyses have concluded that no nuclear explosion took place and that the satellite malfunctioned. Historian Richard Rhodes, who has written a series of excellent books about the history of nuclear weapons, thinks that it was a joint Israeli-South African nuclear test.
The Bulletin of the Atomic Scientists recently published a long discussion of the issue.