Never hearing of a single person being let back sounds more like you grew up in a school district where the parents were wealthy or powerful enough to cause a b

Never hearing of a single person being let back sounds more like you grew up in a school district where the parents were wealthy or powerful enough to cause a big enough fuss that their kids were never left back. The practice seems less common but even if you're isolated in a gifted track of a school you'll still come across the kids who aren't in most programs.