both the b and the c# rows contain the accidentals but in opposite directions of the bellows. the middle 'c' row can be played 'on the row' with the usual gd series of bellows reversals or can be played accross the rows with only 2 reversals.
as an over simplification the c row is like the whitenotes on a piano and the other two rows are the black notes,However it is much more interesting than that as runs like cde can be played accross all 3 rows in the same bellows direction and for example the key of a can be plaayed all in one bellows direction if required - fascinating.
I have never come across a bcc# concertina but can't see any reason why it could'nt be done

cheers

george