If you read (if you have access to it?) the reply from the BMIcc chairman and actually look at what his concerns are, you would see that they are all genuine and serious issues that were not considered or based on incorrect details.
I have read both the report and the BMICC comments (which only came after the BACC published the report).
Like everyone else here, I am not privy to all the information the IRSC are but I certainly found no inaccuracies or cause to doubt their findings.
The BMICC reply states that "speculation and/or unverified information" was used to create the report but they make no attempt to qualify these comments whatsoever.