Back to the original subject:
G9 G7-9 G7+9 G13 (ECT) are all chord extensions; chord substations are chord with different names than the original chord and they do effect the bass note that is to be played.

I feel this should be kept simple so that it can be understood and enjoyed. I am always wide eyed when someone is adding knowledge to my pot; there is always something to learn. This type of thinking makes my performance different/improved then it was some years ago.

John C.