It's natural to doubt. In my case I just asked the UN librarian to verify that the emails posted on the web were in fact of her writing.
Playing JW advocate for a moment, is it possible that, since the above letter is dated January 1992, that the Society applied in 1991 under different guidelines, and became approved in 1992 but were grandfathered in under different guidelines?
I'm not sure why most of the letters say "have not changed since 1991" since it appears that those guidelines go way back. What did change in 1991, if anything?
To me, the problem is not if they used theocratic warfare to get something out of the UN, it's that they lied to the entire JW population by means of that circular letter.