That depends on whether the "original inention" is merely a label on the book. And it definitely is in this case. HP I was written for children. The story was fairly simple, it was no more gruesome than the average fairy tale (before they were Disneyfied) and it was very well possible to let an eleven year old kid read the book, or even a younger one.
HP VII - well, it didn't go so far as to describe brains being splashed on stones or intestines spilling out of wounds, but you wouldn't want your child read a description of a scene where an evil character cuts one of the lead characters' neck open with a knife, or where a snake digs its fangs into another character's neck and the person ends up lying in a pool of blood.
The publisher might claim it's still a novel in a children's book series, but it definitely isn't a children's book.
And if the author shows those parts, and in other places gets into the less bloody and more psychological effects of fear and isolation and oppression, but not takes the time to show the healing required afterwards, I think the author leaves the reader hanging.