The columns will make more sense to you if you use these terms for the columns’ names:
| root | triad | extension or alteration | bass note |
When you’re using the mouse to select these elements it’s not the same as typing or writing in a chord symbol– you have to explicitly select each interval, and the second column refers to the triad only.
In the chord track, the chord editor has a text field. If you type C9 there, you get C dominant 7 with the 9th.
You can customize how chord spellings are displayed in Preferences>Event Display>Chords and Pitches.