We've run across a couple of products in which the manufacturer provides a letter attesting to full compliance with MRc5, but we know for sure it can't be true... take, for example, carpet or paint manufactured in Los Angeles. There's no way that the nylon or latex in these products comes from within 500 miles. However, LEED seems to exempt manufacturers from identifying material sources as long as they claim that it's "proprietary information". As long as they submit a letter saying "it's true", does the LEED reviewer have to assume it's true? There are some major manufacturers playing this game, and I think it's a big problem. As LEED consultants, we try to do our due diligence by requesting more information from manufacturers, but we usually get the "proprietary information" roadblock. Despite pressure from the rest of the project team, we have a hard time submitting these letters as proof of MRc5 compliance. How are other folks dealing with this? Is there any discussion at USGBC about requiring 3rd party certification of manufacturer's claims?