In reply to ce_2015:
I think this figure is not intended to show the evaluation result of every tick. It focuses on taking tick 8 as starting point to show “In other words, the set of matches of te1 or te2 is the union of the set of matches of te1 with the set of matches of te2.” statement.
As you point out, tick 6 has a match and tick 13 has another match. They are not shown in the figure.