For all intents and purposes (i.e. going by the Wikipedia/intro to macroeconomics definition), any form of accounting for changing quality of goods in inflation indices is a “hedonic adjustment.” The BLS distinguishing between “hedonic adjustments” and “cost based adjustments” (the latter of which they do not define) seems to be something specific to them. And the PDF actually describing their methodology for adjusting car prices sure reads like textbook hedonic adjustment to me.