Widely repeated claims from a massively bestselling autobiography are not supported by the historical record.
Great article Jason, I've always been impressed with your analyzing through all of the sources and claims/counterclaims and trying to find the truth from the myths. Although Roberts account is an obvious exaggeration; it feels that even in the most cited/acknowledged Dean books there are cross claims. For example, in the Martinetti book it says James Dean never met Christopher Isherwood, while in the Holley book there's an account from Don Bachardy of Isherwood and Dean meeting at a private screening of East of Eden. I know, it's a relatively small example, but it's just an example of how even in the major biographies there are counter claims and inaccurate information in at least one direction. From all the research you've done with /for your book, are there Dean biographies out there right now that are more accurate/helpful than others?
Perhaps on the same wave length of a Monty Roberts; there's a (relatively) recent book by a man who played T-Bone in Carmen Jones (Sandy Lewis I believe) but who wrote under the name Michael St. John and who also claimed to have known/been friends with James Dean (and just about everyone else in Hollywood) and he claims that he helped set up James Dean with men and women. His Dean story is interesting but I couldn't find any mention of him ever having met James Dean in any source other than his book.
Then onto the least plausible/possible. There's a book by a woman who goes by Di Dean, and who claims to be James Dean's secret daughter (she also wrote a book about Dean under the name of Di Elman). While I see absolutely no reason or evidence to accept her claim as having any validity (and I haven't read her book, but from the amazon reviews it doesn't sound like she provides anything to back up her claims); Warren Beath gave the book a positive review--while also skirting around the what Elman/Dean was claiming by simply saying she has a 'unique perspective' on Dean.
The obvious difference is that those two books haven't sold 6 million copies or have their claims accepted uncritically as true.