We go round the houses in these types of discussions and hopefully learn something along the way. Not to lose focus on the original point and to try and address Chuck's point, the "implied root" depends on the application, outside of apc you might play it under the chords e.g. Bb, D, F on Bb > G, D, E on C resolving to G, C, E on C > A, C, F on F. The key point is the D suspended from the Bb to the C, and really nothing to do with Gsus4.

Way up the thread the original question was what is the difference between C2 (Csus2) and Cadd9. The answer to that question is the only difference is the distance of the 2nd from the root, the notes are the same (e.g CDEG or CEG oct+D). But you can see the note progression could fit by inversion.

However auto play chord works only by note matching, it does not vary the harmony according to inversion generally, as would be the case listening to the piano; apc does not recognise the relative positions of the notes. Thus for apc chord recognition Cadd2 and Cadd9 would be the same.

Each manufacturer has his own system for apc and the Technics system (especially Pianist Mode) is more based on what people play, than on a theory book. For example open voicings of 6/9 chords, and especially 13th chords. In this case, people play a C13 as Bb, E and A (the root is truly implied). Some theory books would give you C, E, G, Bb, D, F and A. Some other products will only recognise the 13th if you play a 7th underneath it. In the case of the Technics system it is reality which is the guide.

Even so, the 13th is ambiguous. Because of the keys keyboard players generally use, the notes E, Bb and D# are pretty much seen as C7#9 (or C7+9). But this is the same grouping (intervals) as the C13, but in the key of F#. So try setting up Pianist Mode, play E, Bb and D# with your right hand. The screen will say F#13 (which is of course correct).

Now with your left hand play a C note (eg: an octave lower than the C under the E in your right hand) Watch the display change to C7#9. Do the same with C13 (Bb, E, A) and then play an F# bass note. The screen will show F#7#9. Then for the hell of it change the bass note to G...Gm6/9.
Chords are indeed ambiguous, and sometimes it is easier to write a complex chord another way. The Technics system may be more capable than most of keeping up with what you do, but certainly in the case of Sus2 the absence of a root from your APC "friendly" chord will cause problems, because the keyboard can't in this case guess which chord you mean (especially because some teaching systems omit the fifth from the harmony to make it 'easier' to play).

So... you can get the Sus 2 'sound' by playing C,D,E,G. The screen will say Add 9. As an example, select 8 Beat Rock, V4 and Mute everything except Bass and Accomp 1. Set the tempo to about 80 and play each for one bar: Bb, Cadd9 (C,D,E,G: our Csus2 alternative), C, F. You'll hear the D note suspended from the Bb chord, and then resolving to C before ending on the tonic of F.

I suppose you could say there can be a big difference between piano type lead sheet chord description and actual apc implementation, and also a big difference in how different manufacturers will interpret the notes you play in apc.

best regards,