> Depends on the person, I suppose?
Probably. In my case long-term memory seems to be really strong down male side of my family so when I read my old stuff from 20+ years ago I remember it and know it was me, just a little different like 'damn, we don't wear clothes like that anymore' when you look at old pictures. The styles/culture/times change you are in and so you adapt to them, but you are still you. I hear this commonly though that some people don't feel like the old them is same person at all.
For me: I have felt a continual sense of self since around kindergarten, before that memory is a little episodic (my earliest is going to hospital to visit my mom and sister after she was born, when I was age 2) but I feel the same 'me' in memories from kindergarten til now over 30 years later. I also do stuff like pick up and start reading a book, put it down, and then go back and finish from where I left off 3-4 years later. I've met a few other people that do that as well, but it's a little uncommon I think?
On the flip side my working memory has always been really bad. My attachment to memory blanks under stress, some people will relate in things like public speaking. I remember in high school forgetting entire marching band drill one time and having to improvise because I stress blanked. The memory is there when this happens it's like it stops streaming to RAM, intuition takes over based on what it sees not what is known.
What is incredibly useful, and this I always felt is for personal writing only (diary/journal)... writing allows for capturing a state of your own thinking/feelings at a time. I would often write to myself when major events happened (good or bad) and then later on I could interpret from the strong feelings what I was going through and see if I handled them or could handle them better. You don't need editing passes for this, it should capture your raw state. Probably good to do this if your memories fade as well, but I don't know. I will probably burn some of my old writing, things that have served their purpose. Apparently it makes you feel relieved doing it and some cultures have this concept.