In a world of unlimited resources, you'd obviously keep moving the threshold down, but according to OP, many jurisdictions were slow to react to the last change

In a world of unlimited resources, you'd obviously keep moving the threshold down, but according to OP, many jurisdictions were slow to react to the last change, and many labs can't deal accurately with very low exposure levels anyway (meaning more limited resources being expended to upgrade these labs). Also, it seems like there are methodological improvements that can be made to observational studies to get closer to an answer for a threshold without literally poisoning people: https://www.ncbi.nlm.nih.gov/pubmed/27009351 https://www.ncbi.nlm.nih.gov/pubmed/27009351