A Canadian man who had been missing for 30 years was found. He had generalized amnesia for a long time.
The BBC: Canada man missing for 30 years found after remembering identity
The man was considered to be robbed of his memory by being struck when he was 21-year-old. He seemed to have vanished immediately after the incident. His mother strongly believed that he was alive, but it took decades to confirm the idea.
Generalized amnesia is a rare cognitive symptom. Patients cannot remember even their name and address. Psychiatric factors are considered to be relevant to its cause. Thus, patients often have something they want to forget.
In many cases, they get recovered within a short term and remember the total memory. I experienced a few patients suffering from generalized amnesia. However, some patients never recover. They have to acquire a new social identity; e.g. social security number, for a living. In such cases, malingering should be distinguished because some criminals pretend to forget themselves for avoiding punishment.
On the other hand, transient global amnesia (TGA) is another category of memory lapse. It occurs after head injury. I think this case is rather applicable to be TGA. However, TGA seldom remains for a long time. So, it is never focused on legal context. Therefore, I am doubtful that brain trauma was the direct cause of his amnesia.
The mechanism of human memory is still under examination. In the future, we can get new knowledge externally instead of a vigorous learning exercise. Meanwhile, we sometimes want to forget the painful memory. Some researchers are devoting to invent a method to eliminate a particular memory. It is ironic.
My past entry: Trauma deleting therapy with electric shock