It really is hard to know if you have issues from TBI. People who become cognitively limited often don't realize the difference - it just seems like everything is harder. Same goes for mood issues from TBI.
It's also hard to predict who will have what effects, and for how long. As a general rule, if someone was to sustain a concussion with brief loss of consciousness, it was the first brain injury sustained, and they began having difficulties following that concussion, the vast majority of difficulties should resolve within 1 year. When you combine mental health issues to that concussion, things get very confusing. Brain injury can cause or exacerbate mental illness and mental illness can complicate resolution of likely TBI residuals. Same goes for multiple concussions, although most of the time changes should have developed within a few weeks of the concussion, although some difficulties may be hard to spot until years down the road. For example, if you have repeated brain injuries with only mild memory loss, will it only become more obvious how much damage it did after you grow older and your brain naturally degenerates as well?