A question about motion path

Hello!. Recently I try to use Gplates to track the motion path of certain subduction zone or trench. However, I found that the arrows of the motion path do not match the trench line with time proceeding. I am sure I have chosen the right reconstructed plate and relative plate. Like here, I calculate the motion of Plate 855 relative to the Plate 857 . The results show that the motion paths did not strictly follow the reconstructed trench line. How could confirm the reasonability of the motion path results on the trench motion?