I realize that Xerox classifieds the 6180 and 6280 toners different -- and maybe that's the end of the story having posed the question in an official Xerox forum. Although I have no plans to buy compatible toners, many of those companies sell one product that they say will work in either machine. That's why the question came to mind. Maybe genuine 6180 and 6280 cartridges are different only because their validating chips say they are. Just musing. Thanks for the answer. We will continue to purchase separate inventories.