On What Account(s) Have Classification Systems for Grades of Concussions

On what account(s) have classification systems for grades of concussions been updated and modified?

A) Updates and modifications are because of the increase of severity typically associated with sports-related concussions.
B) Updates and modifications are because loss of consciousness occurs in less than 10 percent of all concussions.
C) Updates and modifications are because amnesia is found in less than 30 percent of all concussions.
D) Updates and modifications are because the occurrences for both amnesia and unconsciousness are below 30 percent for all concussions.
E) Updates and modifications are because the Glasgow Coma Scale is outdated and not relevant to the signs and symptoms of a concussion.