Each repetitive brain injury is not necessarily a concussion, hence why it's called CTE. It's not chronic concussion encepholapothy, it's chronic trauma. And that's why it's such a tricky issue
"Chronic Traumatic Encephalopathy (CTE) is a progressive degenerative disease of the brain found in athletes (and others) with a history of repetitive brain trauma, including symptomatic concussions as well as asymptomatic subconcussive hits to the head"
Meaning that hits to the head exhibiting absolutely no symptoms may also cause CTE. Even the little hits add up and create, theoretically at this point in time, the tau proteins that are the major cause of concern. The brown portions shown on the middle and right are the tau proteins of two athletes with CTE (football, boxing) and the left is the control group.
