Piano accordions and chromatic button accordions are both keyboard instruments and so the notes (reeds) are controlled by a number of keys.
On a piano accordion, there is one key controlling each note so the number of keys on a piano accordion is usually the same as the number of notes. More keys or notes will make it possible to play music with a wider range of notes or in a wider range of keys.
For a chromatic button accordion with three rows of buttons on the right hand side then unless there are any “dummy buttons” (sometimes added for reasons of vanity) it will also have one key (or button) controlling each note and so on a three row button accordion, the number of notes will usually be the same as the number of keys. As with piano accordions, more keys or notes will make it possible to play music with a wider range of notes or in a wider range of keys.
For a chromatic button accordion with more than three rows of buttons, each extra row usually duplicates one of the other rows i.e. when you press a key from the duplicate row or the row that has been duplicated, they play the same note. So when an accordion has more than three rows (usually four or five) of button keys then the number of notes available will always be less than the number of buttons. More buttons than notes makes it possible to play the same note in more than one place on the keyboard and can make some music easier to play by giving an alternative choice of fingering.