it’s simply that Back has nothing to gain to claim to be Satoshi. It would make bitcoin a lot more volatile. He even said just now

> I also don't know who satoshi is, and i think it is good for bitcoin that this is the case, as it helps bitcoin be viewed a new asset class, the mathematically scarce digital commodity.

That’s as close to admitting it as you can get

Point being, he has a lot to lose if people think he IS Satoshi.

I would be coughing up those email headers if I were him. Or forging some, if necessary.