Very few concussions are ever diagnosed by a doctor. It is only the past few years that a doctor 'diagnosis' has become common. This is because teams have had to implement concussion protocols for liability reasons and the movie Concussion.

The risk of undiagnosed concussions or ignored concussions is that the person does not take a break to allow the brain to recover. Studies suggest that those low intensity hits that are repeated (hockey, football, etc) without a break from play or practice are the most dangerous. These are mostly sub-concussive impacts without even a need to shake it off.

I think you need to consider the various peak risks of each activity. No contact hockey reduces the repeated body checks and knock downs from them but leaves you with falls and pucks to the head. So, you have reduced many of the risks. Mountain biking trails have risk levels to consider.

Then, consider whether you have adequate disability insurance compared to the risks you decide to endure. Risks tend to have an exponential increase in long term injury or disability as the intensity increases. A fall at 30 mph is substantially more injury risk than a fall at 20 even though the speed is only 50% more. Add the greater ability to recover from a near fall at 20 vs 30.

So, only you can calculate the risk to you.

btw, I learned that helmet padding has a limited life. Check yours.