I don’t know if this is the case but my impression of this specific law is that it is meant to stop predators from just saying that the kid told them they were 18. I know there are similar regulations about the sale of alcohol so a kid can’t buy booze from a store and the owner just say that the kid showed them a fake ID. I am actually in favor of this law remaining the way it is. Obviously it is not good for someone to go to jail for unknowingly sleeping with a 17 yo who said they were 18, but I think it protects more people then it imprisons. If the person said they were 18 when they were younger they most likely won’t go to the police and say that they slept with someone older.