At the time there was no diagnosis for brain death for Karen Ann Quinlan. Her autopsy supports what you are saying in that much of the brain was not severely damaged or “ dead” but some areas were.
Until there is an autopsy on Jahi McMath your statements Comparing the extent of brain damage between the two the are a matter of speculation. And zero details of the examination have been released, so you are overstepping in making any detailed comments. You are inferring things based on the conclusion that she is brain dead and that is fair and reasonable.
I personally believe she is brain dead because I trust the professionalism of the medical staff and their sincerity and know that the advances in understanding and diagnosing brain damage and brain have become quite sophisticated, in no small part due to the Quinlan case.
As far as your Quinlan comments, her brain was irreversibly damaged and was not “fully alive” and had regions that were dead, hence her state.
Any detailed comments I have made are based on the definition of brain death. They do not have to be specific to this case.