When I worked for a national (USA) electrical testing company I was stuck being the safety coordinator at our branch (in southern California) for a few months, this issue came up and I dug into it a good bit, mainly because I had a couple of techs who saw the same label and refused to handle any of our extension cords.
First level fix, you can find industrial cord, like SO or SJO that does not contain any lead, get a couple of ends and make your own cord. That should take care of those who think Prop 65 labels mean death is near. I also bought two different types of lead test kits, and checked a number of new and old cords with the Prop 65 labels. Guess what, not one of the test kits recorded any measurable lead.
As noted above, lead is added to some PVC and other insulation materials, from what our safety consultant found out, lead is something that Prop 65 requires a warning if ANY lead is used in the components, fabrication, coating or finishing.
So don't chew on it, if you drag it across the ground of course you should wash you hands after handling it. If a cord shows signs of insulation deterioration, like cracking, chalking, etc, get rid of it.
My two cents worth. Mike L.
