it looks like you'd add dashes for the tails, just like you would for a semiquaver on paper. one of the great things about this is that there's zero 'design' to sheet music, its essentially a spec. There's a lot of implied information that can be fed into the handwriting recognition, and it looks like it doesn't try to parse until you've moved onto the next bar, so can analyze the block against a very well defined domain. Vertical lines all represent a note (besides small ticks for sharps maybe), and the time signature narrows this down to only so many possible permutations of possibilities.