Yes, half the people have less, half more. But even the "more" half is very bad news. 5-year survival is ~4%. My dad made it something like 16 months, although his quality of life was quite poor for most of that; the tumor had already caused some neurological complications, and the surgery kicked off frequent seizures that were debilitating. From what I've read, poor quality of life is typical of aggressive gliomas, even when in nominal remission. And then there's the half who have less; my mom got about 4 months, most of which was taken up with radiation and chemo.
Please let me know in the future if I can bring up any of my prose to your sensitivity standards. That's a big concern of mine when writing on the internet.