How often are bumps to head really concussions? is just a headache for a day or two after a concussion? do these mild hits and bumps cause cte later?

Variable : Not all bumps, blows or jolts to the head or body lead to concussions. Headache is a symptom of either impact to the head/skull or the jolt to the brain and hence can be a sufficient but not diagnostic marker for an actual concussion. Post traumatic headaches at times can persist for months to years. CTE is seen rarely in repetitive head injury without even a single diagnosed concussion.

Concussion.: Not every bump to the head, however strong or light, will lead to a concussion. A concussion is suggested by a specific set of symptoms that spans the day or two after an episode of significant trauma to the head. If these symptoms are not present, then it’s probably just a bump to the head.