In the early '80s, the state of the music was such that Top 40 evolved to nearly AC. About the only band that wasn't AC, was "Foreigner"! As a result, many Top 40 stations stayed at that level and a new generation of Top 40s(renamed CHR)sprang up to take their place, starting around 1982-83. I'm surprised that any of the older Top 40s survived the transition.