Since the Ming and Qing Dynasties,there have been many criticisms and explanations on the plot mistakes in The Tale of Pipa,but they neither probed into the cause of the mistakes and nor provided detailed evidences,which makes it impossible to reach a justifiable conclusion.

A general procedure for labeling and completing an imperfect line drawing is given,and an example shows how to utilize the line labeling and junction labeling information to predict and recover the missing junctions.