As I understand it, “sus” always refers to the 3rd that is to be replaced by the interval that follows, hence sus2 I - II - V or I - V - IX and sus4 I - IV - V.
I don’t know of sus chords other than sus2 and sus4.
Put differently: A sus2 chord is an add9 without the 3rd.
Because in practice the 2nd is rather a 9th, at least for guitar players.