Not entirely unrelated. Exhaust catalysts are easily "poisoned," by lead among other things. Leaded gasoline would do it, so modern catalysts would never have been fitted to cars permitted to run leaded gasoline (very relevant during the time when both leaded and unleaded were available). Or put another way, the "unleaded only" signs you see on some older cars was not because the cars wouldn't run, but because running leaded gasoline would quickly degrade the emissions control equipment (oxygen sensors and catalysts primarily)