An assertion that X happened in the past is fundamentally different from an assertion that X exists.
The certitude one can achieve through evidence for (or against) the claim that the Earth is presently flat, can never be obtained for an assertion regarding a past event.
The certitude one can achieve through evidence for (or against) the claim that the Earth is presently flat, can never be obtained for an assertion regarding a past event.
You're mixing apples and oranges.