My son was adopted as an infant. He knows all about it. He’s Korean, its pretty darn obvious he isn’t our bio child. He never talks about it. Never really wants to talk about it. It just isn’t his thing. We talk about it around him from time to time (and his sister does - she’s fascinated by the whole story). So I think its possible he does sort of remember it enough to have pieced together parts, but its not a big enough deal to talk about it or he isn’t comfortable with it. And if that is the case, its probably important to talk about it with him, because kids tend to fill in the blanks by making shit up - and he might believe a lot of stuff that aren’t true.