Yardeni model uses Moody’s A-rated corporate bond yield. Which ones are A-rated? Aaa, Aa1, Aa2, Aa3, A1, A2 and A3, altogether? Or maybe A1, A2 and A3 only? Please shade some light here and elaborate if I miss something important here.
For the exam I am sure you will be explicitly told long term A Rated Corporate Bond Yield.
But you have a valid point. Practically when yield curves are presented then one of the presentations is showing average yields of range of ratings such as yield on Aaa - A rated corporate bond yield = x% which may be used for Yardeni.