A friend of mine asked me to tab one of his songs and there is this part where he plays a simple voicing with a "Cadd12" followed by a Cadd11 and a Cmaj.

The thing is: the 12th of C is the same as its 5th (G) played an octave above, so it shouldn't be in the chord's name. My problem is that the voicing is a big part of the song and I can't simply name the chord a Cmaj.
So, do you think Cadd12 is valid chord name in this case?
if it's tabbed out you shouldn't have to give it a stupid name. just notate the range on the sheet (or tab i guess) and the voicing should explain itself better than someone seeing "Cadd12" would lol
Thanks for the fast reply. But for a matter of curiosity: What if there was no sheet and only the chords' names?
Then you'd have a very inefficient method of transcription.
lol, I know. I think what I'm trying to say is:

This damn thing really excited my curiosity and I want to know if is there a situation where a Cadd12 would be a valid chord name?
lol, I know. I think what I'm trying to say is:

This damn thing really excited my curiosity and I want to know if is there a situation where a Cadd12 would be a valid chord name?

Add12 is not an extension or alteration to a triad, so you would never use it. Transcription by way of chord names or roman numerals is second to either tabbing or the standard notation.
Why do you need to say "add12", when you've already tabbed the voicing or used a chord chart for it or whatever?
If I were you, I would tab every chord and different chord voicing at the top, and notate your different C chord differently. Something like this:
C............C(G)
e|-0----------3----
B|-1----------1----
G|-0----------0----
D|-2----------2----
A|-3----------3----
E|-------------------

That way when you are doing your lead sheet along with your lyrics, you can write C(G), and the person can look at the chord library you have written at the top and see what voicing to use. I guess I "get" what you're saying with C add12, but musically it makes no sense to notate something that way.
No. There's no point.

First of all when you have an ADD it implies a voicing that has upper extensions, past the 7th, but has no 7th. This means the triad is already present. The 5th is there. There's no ADD, regardless of the voicing. I'm assuming your moving the voicing of the 5th to the B string. So, if you're tabbing by way of explanation, its simply x chord, no add, and notate the shape of the chord, in the TAB itself.

3 x 5 4 3 x would be a G where the high voicing would be the 5th, for instance. If additional or specific information is needed, it goes in the tab or a chord grid, but you don't change the name. and it's certainly not an ADD chord.

Best,

Sean