Now that is a really good question.
Either:
1 - Brittany Ferries have excellent resource management, and they have reprofiled their timetable based on intelligence on the anticipated disruption,
Or
2 - They are undertaking some early customer expectation setting, and there could be changes and more significant impact to come,
Or
3 - They aren't that good at customer management or resource management and they have done a "best guess" on what happened last time.
Aricus