So, thank (belated) for the downloads in the chord explorer series. I was trying to make sense of each chord’s notes and how that relates to their name. I get it, except for the difference between add9 and add2. With Gadd9 we have the notes GxDABG. Why wouldn’t this be called Gadd2 because we are adding an A to the triad of GBD? Instead we pull out the 9th note in the scale? Another question that falls into the idea of naming, why G6 instead of Gadd6?
I think these are mostly down to the presence/absence of the 7th in the chord. These articles may help you understand the various types of chords better: