I literally forget my own name from time to time and I'm not immortal, I have been alive only 23 years as matter of fact.
Why does it happen to me? Probably because I never use my name,I never meet new people and no one ever calls me by name.
I guess it's just normal to forget useless things, your uyou don't need trauma to forget.
I might say psychological trauma makes every memory more vivid, and physical trauma to the brain is often unpredictable since even people with half a brain can remember everything, your memories can easily be stored in another place if part of your brain is destroyed.
A brain is like an arm, if you lose your main arm you don't forget how to write, you learn how to write with the other arm.
Oh sometime I forget my own birthday and it takes me a while to remember it, since I only celebrated it once, when I was 6.