Because when McCoy was launched there was a lot less characters in the game. As more characters come the names need to be more specific. Several episodes involved McCoy and Kirk being imprisoned, so in order to keep that name available for future use Kirk's name had to be more specific than "prisoner". When McCoy was released back in the mists of time, this wasn't a particularly important detail and thus not considered for him.
Comments
Rura Penthe Commadant
Rura Penthe Reed
Rura Penthe Kirk
Rura Penthe McCoy
Martia