These buttons are there purely for decoration. With the extra buttons the pattern can be made complete (5 rows having n, n+1, n, n+1, n buttons which does not correspond to the diagonal layout of the real notes) and a large empty space at both ends of the keyboard can be avoided. Not only are extra (non-functional) buttons added, the size and spacing of the buttons is also different depending on the size of the accordion versus the number of notes it has. For instance, I used to have a Bugari 505/ARS (46/120) and still have a Pigini bass accordion (large instrument with 40 playing notes) and both have the largest size of buttons. My wife plays a Bugari 508/ARS/C, generation 2008 (the newer ones are different!) which is a bit smaller than the 505 and has smaller buttons but the same number of buttons (and notes). Then we have a small Bugari 504/ARS/C with 52 notes and my larger AKKO with 64 notes and these have yet smaller buttons.
My Hohner Morino Artiste XS does not have any fake buttons and has the standard layout. Because the notes come in a diagonal pattern (mine is C system) it means that the lowest note available is only on the 4rd row: a low A. The lowest note on the 1st row is C. Having the A on the 1st row would break the n,n+1,n,n+1,n graphical pattern of the keyboard. My AKKO has no fake buttons and this is done by not including the 1st button of the n,n+1,n,n+1,n pattern on the 4rd row.
