On the other hand, just keeping to the observation, we can at least say that countless pathologists and others over a very long period have failed to identify t

On the other hand, just keeping to the observation, we can at least say that countless pathologists and others over a very long period have failed to identify this anatomical entity. In the main it seems that experts see what they expect to see and if it's not in the anatomy book then it doesn't exist. That's not necessarily perjorative. It's how we humans tend to be when observing the world (including ourselves) around us.