“As part of its preliminary review, the ICIG did not request access to records of the President’s July 25, 2019, call with the Ukrainian President,” Michael Atkinson, the ICIG, wrote. “I decided that access to records of the telephone call was not necessary to make my determination that the complaint relating to the urgent concern ‘appears credible,’”So the IG never actually bothered to read the transcripts of the call between the two Presidents before making a determination if the allegations regarding that specific call was "credible". That seems like an inconceivable slip up of the highest magnitude. Literally no reason in the world not to review the call to see if it matches your allegations. Not sure if this is just pure incompetence at an extreme level or that Atkinson was just more intent on getting this complaint to Congress (right or wrong) than doing his job.
The fact that the Office of Inspector General is actually defending this nonsense to the public tells me that they either were not really paying attention and are now playing a massive game of CYA, or that there were people in the IG office all the way up to the top that were bound and determined to get this rogue complaint to Congress.