(Cheers for title edit)

Wotcha confused by Lara?

Those definitions are broad, but are what are used to diagnose. I think the general idea, the difference between a concussion and m/TBI is that in a concussion the brain is not directly injured. With m/TBI it is. This is why those time frame windows for healing are given, though by no means an explicit certainty.

This, of course, as is evidenced by all the folks commenting here, not to say that subsequent swelling does not cause symptoms from a concussion. This is where genetics and underlying conditions come into play. If someone already has neurological issues (OCD, migraines, epilepsy et al) or a poor immune system or an inflammatory disease or some such, this can cause latter events in the cascade to manifest as stronger symptoms as the underlying issues are exacerbated.

A big factor in this is receptor overload (which ever receptors). When the info flow is broken the brain can interpret this as a threat (/stimuli) and produces an unnecessarily strong response. This is why PTSD is often associated with head injuries, even though it is often not 'true' PTSD (a key part of that definition is the complete sensory memories of the triggering event linked to adrenal surges.)

The systems of the body, and certainly the brain!, are very much interconnected. This, in part, accounts for the variation of healing times.

(As my post was so long, and we all talk about it here so much, I did not include every symptom but of course they exist.)