Shorelines are known to change a LOT, whereas reef edges change slowly. Looking at the various aerial photos of Niku over the years, the tree line can be seen to change distance from the "beach". Also, there is an easily observable change in vegitation at some distance from the beach, likely due to storms washing away the intermediate foliage, which also changes the observed shoreline.
I think the shoreline is a poor choice for reference. The Norwich City location is a better reference, but may have changed heading. The reef edge will also have changed, but slowly, as I understand. We need an expert on the subject.