Excellent question. These documents are now in the public domain for any agency or news organization to investigate. So far, no one (cough, cough MSM) has been able to prove them false.
I'm not sure how a news agency would prove an internal Iraqi document false, but I would like to see the US Govt stand up and say, "They're real", then provide the evidence that supports the assertion.
When these documents were released, the disclaimer at the top of the web page said that the US Govt. had neither authenticated the documents, nor did they validate the information the documents contained.
So, absent this authentication or validation, I would personally suspect anything released by the federal government and am surprised to see everyone rally around unsubstantiated claims promugulated by the government itself.