Are you with Leibniz or Cicero?

[Mudhammam]

You're obfuscating the point and I think it's intentional. You are skating around absolutes. I am not required to remember all of my past experiences to retain what can properly be identified as me, but I cannot be without those experiences. Those experiences inform my future actions even if that which I am able to recall are hazy imperfect facsimiles of actual events. The fact that I may not remember a majority of what I have experienced does not delegitimize what it is I do recall or make insignificant forgotten events and the impact on my present personality. The intent with which you use 'majority' here is what cautions me as to your motives. The underlying assertion that there can be no 'I' unless I can recall >50% of my past experiences is ludicrous.

As far as people suffering brain injuries and their personhood, I can only answer based on my personal experience. My mother has suffered Alzheimer's. For her sake, she completely succumbed relatively quickly. Her gradual disappearance was painful to experience, despite how fast we were told it was compared to others. I can definitively say that there is a human body that has a remarkable resemblance to my mother, but my mother no longer exists. Redefining personhood for the convenience of argument won't change this fact.

By the way, you didn't answer my question.

So, let's say you become vaguely suspicious tomorrow or at some point in the future that once you lived in a variety of former times and places, under a different name and face, and that's the only detail about this peculiar epiphany that you can recall. The only difference between that situation and 95% of our own lives, especially events that we experienced in infancy and childhood, is the continuity of our name and more importantly, the steady recognition by others who identify us as that same individual. But if those whom you thought were family, friends, acquaintances, etc. were to suddenly start treating you as if you were a complete stranger whom they had just met for the first time, as much as you might find yourself confused and distressed by their behavior, you would probably not concede that you were not the same individual that you believed yourself to be prior to the change in them; yet if on top of that you woke up with no recollection of any past events in your life, and everyone continued to act as though you were someone they had never met, then you'd be precisely in the situation wherein you wake up at the termination of your present life in the body of a newborn. In other words, there still might be a sense in which "you" retain your "you-ness," even if everything about you is radically different. My answer to your question is that I don't know how much experience and knowledge is required of past selves to form personal identity (I like your idea that it must include "experiences [which] inform my future actions," but I might add that at most it need only be a perception of past experiences, not ones that have actually occurred); if it's merely a vague notion that is required, then you can assume at least as much as I did in the sentence that began this reply.