Critics are totally unable to prove that the Admissions (also called the Affirmations), supposedly written by LRH, are authentic.
Indeed, the sole source for them is Gerry Armstrong, who supposedly received them from an unnamed source, supposedly re-typed them, then supposedly destroyed the original copy he received!
As to why he destroyed the handwritten copy that would have proven it coming from LRH is puzzling, except of course if it just is a cover-up to "explain" why he can't substantiate their origin and possibly just made it all up.
He claims he destroyed it for copyright reason, but this does not make much sense. At the time, Armstrong was already a fugitive from American justice because he walked away with the $800,000 he received from the CoS as part of a settlement that he repeatedly violated. Publishing the source of these Admissions or at least preserving it would not have made a difference for his case, whereas publishing them as proof such a damaging document indeed comes from LRH would have made a huge difference regarding the Scientology issue.
In this respect, the possibility that Armstrong actually wrote these Admissions himself is not that remote.
Here is a good post from this thread that summarizes the situation.
Related blog entries: R-Affirmations-