I don't have an answer either misslabarinth as to why some will remember some incidences and others won't remember as much

I thought the block out of memory was some sort of internal protection measure that some will develop.

I also think it relates to PTSD; whether or not this develops at all because certainly not all do.

None the less I found this quick article on PTSD for you here on PsychCentral - it makes mention of memory:

Understanding the Effects of Trauma: Post-traumatic Stress Disorder (PTSD) | Psych Central

I hope it might have an answer for you there

Researchers, Clinicians Still Differ Over Repressed Trauma Memories | Psych Central News