Some little bits of knowledge I've picked up over the years: My own pile of Columbia frames shows a few different styles of headbadges as well as frame construction. For example, nearly all manufacturers changed their metal headbadges to foil stickers at some point in the later years of American production or as Taiwan or Chinese production begins. Once these basics are complete, hopefully we can get into some specifics within brands that will help identify years of manufacture more closely. It does become necessary to do this kind of cross-referencing to identify what it is that you have found. So many bikes of the types we are interested in have lost identifying marks.