There are some studies on the internet. Just google it.
I read a book 5 years ago that had a chapter devoted to the subject. I have had sever conversations with my IC about it.
The problem is the person usually does not want to remember.
They compartmentalize things and want to forget.
My FWW did just that. Even regression therapy was not completely successful.
Hypnosis is a possibility that my IC said may or may not work so I did not press the issue.
I can remember things that happened over 40 years ago. Maybe not in great detail but I do remember and I can see the images of what happened to me still. But I did not compartmentalize and try to forget. I believe you need to remember no matter how painful that makes us who we are and makes us stronger. But some people can not deal with some things they did or things that happened to them so the block it out and choose to forget. Either it is painful or brings on guilt and regret and they think poorly of themselves.
If I can find the book I will post the name for you.