Lead is a good example. Lead is everywhere, and we can measure it down to very low levels. There are a lot of things you can't label as lead-free, but you can label when there has been an intentional addition of lead. First of all, there should be no intentional addition of lead, and usually the levels in regulatory limits, 90 parts per million, are set to make sure that this is the case. Generally, if someone is going to make a product that is going to use lead, it's going to be a lot higher than 90 parts per million. If it were an intentional addition of lead, such as in electrical wires, then it is appropriate to have a label, since if you are handling electrical wire, lead is going to come off on your hands.
As for labelling fatigue, it is one of the criticisms of Proposition 65, and we can learn to do better. There have been three different members of the committee since the last peer review of Proposition 65. I brought a report that includes some of that.