We'd never even heard of "Lost" before it was out. We knew the demo, yes, but the final song is so different it almost doesn't count. We barely even recognized it because the vocal hook had completely changed and had no idea it'd gotten as far and as polished as it did.
I'm just one person and I make a minimum of 55 demos a year as a hobbyist (one a week!), I can't imagine what sits on LP's drives that they just haven't told us about. Most of it terrible, but some gold that just didn't quite shine brightly enough for sure.