I run across the statistic occasionally, but I don’t usually try to keep track of it. My recollection is that head shots are only fatal about 98% of the time. The rest of the time the bullet either deflects off the skull or doesn’t actually do lethal damage to the brain on the way through. I’d assume this includes cases where there is serious brain damage, but the victim survives anyway.
Either way, there’s a mountain of medical cases where someone gets shot in the head and survives in some condition for any number of reasons.