None of the answers offered answer the question. As I understand it, OP is describing a situation wherein if the potential defendant has not been informed
then he is not liable, whereas if he has he becomes liable. I cannot think of any term to describe this, nor do I think it matters. Donohue v Stevenson is the classic foundation case for the tort of negligence; its principles are still valid today. If Barmaid, a current practitioner, is looking in, then she may be able to help further, but I, for one, I stumped.