Your argument that nothing is private unless you can prove it wasn't perhaps published elsewhere is a fallacious
isolated demand for rigor.
Except that "nothing is private" strawman isn't my argument, which is actually "there's no way for anyone, other than Satoshi or the original sole recipient, to tell if a block of text already out there with just Satoshi's name attached was intended to be private".
If someone received something in private email it was private. Yes, in theory it could have been published elsewhere-- people should feel free to go FIND those published copies.
Thank you. So what people will be finding out there RIGHT NOW will be a mix of A) private emails, whether they've had their headers stripped (or modified to appear to have been sent to a listserv) or not, B) stuff Satoshi self-published, and C) words attributed to Satoshi that Satoshi never communicated.
And I would posit that the OP will not collect even one single, authentic, private email more than what's already out there. Why would people suddenly decide NOW to break confidence, after more than 8 years?
P.S. Were Satoshi's emails DKIM?
Out there=on the public internet, cached on who knows how many search engines, archive sites, personal computers, ...?