That does not mean Hammesfahr isn't an excellent doctor.
Also, a PVS diagnosis isn't something that can be meaningfully judged by majority opinion. All a diagnosis of PVS means medically is that a doctor hasn't found any type of stimulus that could produce an observable cognitive response. A doctor who doesn't look very hard isn't apt to find anything that's not blindingly obvious. But if two doctors (or even one) finds congnitive responses to a stimulus the fact that some other doctors don't hardly proves those two wrong.
If a doctor who claims to have found a response is accused of 'wishful thinking', the proper protocol would seem to either have a disinterested person document the behavior if it's easily observable, or else use a double-blind protocol to validate it. The doctor seeking to disprove PVS should be allowed experiments to refine the protocol as needed.
Sample protocol: have a tape prepared with a random sequence of the words "relax" and "get tense", spoken in a uniform tone of voice and spaced at five second intervals. Record the patient's reactions on a polygraph with a mark at each five second interval, and on video with a light that likewise blinks. Have the doctor watch the video without sound and try to identify which words were "relax" and which ones were "get tense". If the patient is responding cognitively to the words, the doctor should be able to tell. If not, he'd have a hard time guessing above 50%.
Note that all of the 'interpretation' in this protocol is done by a doctor who wants to find the patient non-PVS, but no amount of wishful thinking would allow him to determine cognitive function when one exists.