Re: ST VI:TUC Out of character for McCoy?
Well for decades prior to that, it's unlikely the Klingons shared medical data on their species with Starfleet or had a physician exchange program. However, with a quick scan of Arne Darvin, McCoy was able to determine he was a Klingon. But that doesn't mean he was familiar with their internal organ structure.
Dr. Howard, Dr. Fine, Dr. Howard: For duty and humanity! --Men in Black (1934)