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It is fair to edit answers until June 10th 12:00 UTC, the end of eligible guessing.

The prediction is about July 4th, which is long after that. :)

Because the block chain knows all edit history.

I was sure somebody would give that answer :)
But it would be better if the 'edits' are easy identified from the steemit users as well, and not only from the blockchain "experts"... something like a drop down menu for each post/response that has a edit history... Because new users could be confused and sceptical about prediction posts like this because they don't know about the blockchain technology behind steemit... So a "permanent" edit history option would make sense I think....

steemd.com displays (edited) when a post has been modified/edited

I know that.My point is that everything must be super easy for new users. We should not need to explain them how to find this stuff "outside" the steemit platform....