Kind of like how I can't remember a thing about a rafting trip I was supposedly on when I was 19, but I clearly remember running into someone I was on that trip with, and discussing/reminiscing about it, when I was 22. So at 22 I clearly had the memory (enough to talk in detail about it), and I now (more than 20 years later) have a recollection of that conversation, but other than that the memory of that trip at 19 is totally purged. (except some vague recollection about glowing moss in the woods).