I was just on Wikipedia and the article there states in a couple places that C2 is the same as Cadd9. Which means using C2 when you mean Csus2 would be wrong or confusing...
(of couse it could be the wikipedia article which is wrong or confusing)
http://en.wikipedia.org/wiki/Chord_n...#Chord_quality
"Names and symbols which contain only a plain interval number (e.g. “Seventh chord”) or the chord root and a number (e.g. “C seventh”, or C7) are interpreted as follows:
If the number is 2, 4, 6, etc., the chord is a major added tone chord (e.g. C6 = CM6 = Cadd6) and contains, together with the implied major triad, an extra major 2nd, perfect 4th, or major 6th (see below).
If the number is 7, 9, 11, 13, etc., the chord is dominant (e.g. C7 = Cdom7) and contains, together with the implied major triad, one or more of the following extra intervals: minor 7th, major 9th, perfect 11th, and major 13th (see Seventh chords and Extended chords below)."
//
"Notation must provide some way of showing that a chord is an added tone chord as opposed to extended. There are two ways this is shown generally, and it is very common to see both methods on the same score. One way is to simply use the word 'add', for example:
Cadd9
The second way is to use 2 instead of 9, implying that it is not a 7th chord for instance:
C2"