Let's consider another example.
We may need ...
And the trajectory on the left is encoded into the binary sequence on the right, using the two sets of "peaks and valleys" shown below.
The first five flat tiles t[0], ..., t[4] of the trajectory are encoded using the left Ps&Vs. But the 6-th tile t[5] colored blue is buried under peak Pa as shown in the middle figure. Thus we need another set of Ps&Vs shown on the right to encode the rest of the trajectory.