In 1972, Lewin claimed that he had written not just the introduction, but the entire report, as a hoax.
More on the cast of characters in this hoax is at http://www.simonsays.com/titles/068482390X/cast.html, and of course in Lewin's self-review from the New York Times.
Upon its initial 1967 publication, Elliot Fremont-Smith of The New York Times said "It is, of course, a hoax -- but what a hoax! -- a parody so elaborate and ingenious and, in fact, so substantively original, acute, interesting and horrifying, that it will receive serious attention regardless of its origin." The Report from Iron Mountain must be viewed as the same type of document as "Silent Weapons for Quiet Wars" - almost surely a hoax, but nonetheless "Since the document is explanatory and academic, simply presenting foundational concepts and analysis, its source is immaterial in terms of the utility of the document, though it would be a separate and dramatic, though unsurprising, revelation if it were proven to originate with an actual circle of power brokers in government and industry." (quoting from my introduction to this compilation).
Larry Abraham, the author of The Greening, apparently believes that the Report from Iron Mountain was the product of an official thinktank project, and is either unaware of or rejects the stance that it is a clever hoax. On the other hand, Abraham may be personally convinced that the Report is a hoax, but sees the advantage in continuing and embellishing the now-dog-eared ruse. Regardless, Abraham offers many illuminatory observations in The Greening, which are supportable, free-standing, and completely independent of the Report's pedigree.