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.
Curly: Moe, Larry, the cheese! Moe, Larry, the cheese! (Horses Collars, 1935)