If it were 1969 it might have been some kind of new federal regulation regarding the loudness or even the frequency range, but if it changed at all between 67 and 69 it would have been some arbitrary thing like the tone, unless they changed to a new supplier. All the Mopar horns I am familiar with seemed to be exactly the same, but then the newest cars I have worked on are 67s, so I guess I wouldn't know. Usually, when these kinds of questions come up, I go to a Mopar show and look under the hoods.