Arturo O. answered 01/30/18
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This is a very vague question. However, as someone who reads a lot of history, I can tell you that historians consider 50 years after an event to be the time it takes for legends and embellishments to find their way into historical accounts. The important thing is that the account be written within the lifetime of eyewitnesses, who could still be around to refute inaccuracies, myths, legends, and embellishments that arose over time. In your question, 20 years is close enough to the event that eyewitnesses are still alive who can attest to the accuracy of the account.