An overtaking situation might not be clear cut every time. Take for instance a classic dilemma where two vessels whose speeds differ marginally are on a converging course.
One vessel could treat it as a crossing situation and the other as overtaking. Any ambiguity has to be resolved by assuming Rule 13 (Overtaking rule) applies and the vessel with the greater speed should act to pass the other at a safe distance, and conditions permitting astern of her.
Loss Prevention Poster When in doubt, assume you are overtaking