Again, we were on different sides of the continent, so mileage may vary, but it was clear, from the time I entered the business in 1971, that the first generation of Top 40 listeners were not interested in "graduating" to MOR, but that several records Top 40 played, from Donny Osmond to Led Zeppelin, as well as a teen-centric approach to jock content and promotion, weren't working for them anymore.
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Black music and Latin-influenced music (Santana, Malo, El Chicano) was not only welcome, but essential. If there's one place where AC PDs tended to play it too safe, in my opinion, it was there. But I had the advantage of being a native Californian and the radio without that music was just out of the question.