Chord Symbols: add2 or add9? (includes my video on using added ninth to chords)

Hi everyone!  I received a question online today (on my YouTube channel), an excellent one, and one which is subject to debate.  The question is in response to one of my videos about using add9 chords on piano.  (A link to the video is included below.)

I thought I would share the thread here:

VIEWER: Isn’t the D in Cadd9 supposed to be an octave higher? I guess I’m just confused as to why it isn’t Add2 instead.

ME: Hi Jordan, this is a very good question, and one that is subject to debate. Technically, the voicing of these add9’s that I am using here are really “add2”. In general practice however, add9 is favored in chord symbols found in sheet music, and is meant to imply add2 or add9, depending on the voicing choice of the player. It’s interesting to note that add9 chords played on guitar have the ninth tone on top sometimes, and sometimes the 9th is not the highest tone, often depending on ease of finger positions. This is also true in a piano player’s choice of voicing. Again, to recap, add9 technically has the 9th as the highest tone in the voicing, as you indicated, but when using chord symbols, add9 is preferred for either one.

 VIEWER: That definitely makes more sense. Thanks for the clarification.
ME: Certainly, your question is much appreciated! Two other interesting points: A very popular, jazzy left-hand voicing for the MINOR 9th chord (as in Am9) — which, by the way, is NOT an add9 chord, because it also contains the 7th (I talk about that difference in the video) — is this, using Am9 as an example: G, B, C, E, where the root is implied, and can be played before or after the first cluster (or covered by the bass player). I bring this up because here you can see that the “9th” is not the top note in that particular voicing. (You might try that out, it sounds very cool!) Another thing: In my full two-handed voicings in the video, such as Cadd9, left hand plays C and G, and the right plays C-D-E-G. On close inspection you will note that the 9th (the D) is actually voiced far above the root (the left-hand C). But that is not mandatory to voice add9 that way, just a certain nice-sounding choice.
 Here is the video lesson which prompted the question:
 See ya soon!