Why? I remember using a simple program in 2000 to see how many moves were canonically required, and most positions I came up with were resolved in 13 moves.
On the other hand, I would have thought 19 steps were enough because they already cover the full space of positions. To wit: There are 12 possible choices at each step, 19 steps cover 12^19 possibilities, which is 8 times more than the 43,000,000,000,000,000,000 positions.
