> I remember my first day at school vividly
That would be a memory of a memory. Not a true memory.
For example, for my first day at primary school I remember that my parents asked me to remember my religion, which was presbyterian. I went to school that day worried that I couldn’t spell presbyterian, and was surprised and delighted that they not only didn’t ask me to spell presbyterian, they didn’t even ask me what my religion was. :-) A memory of a memory, not a true memory. I remember literally nothing from primary school days.
> 4. “I’ve seen/heard that before” type memory. For example recalling a tune that I haven’t heard for a long time. I can know that I’ve heard a tune or seen an image before even if I haven’t seen or heard it since high school and probably much longer. This is the sort of memory that allows me to remember tunes, words, letters, pictures and mathematical methods long after I’ve forgotten the context in which I encountered them.
For example, on 29 Apr 2016 the tour bus driver put on a collection of Australian folk tunes. For one of them “Ryebuck Shearer” I was immediately hit by the immense length of time since I had previously heard it. I knew all the tune and half the words perfectly but I had previously heard it so long ago that I couldn’t remember when, it’s hasn’t been on any radio station I’ve listened to in memory, I didn’t encounter it at the Tamworth Country Music Festival 15 years ago, or when I went looking for the folksong “Queensland Ladies” in the 1980s, I never learnt it in high school, and my parents never had a recording. So when did I learn it?