Satoshi did NOT correct it. His P2P foundation account was hacked, just like his gmx email.
His P2P Foundation was hacked afterwards and then locked for good; but P2P Foundation confirmed at the time that as far as they could tell, it was Satoshi.
Was it signed? I was following pretty closely and my version of history also had that as being fake. This is one instance where I would love to be wrong though.
It was not signed, because Satoshi has never signed anything ever. But it was, as far as it's possible to tell, genuine.