How are you searching? if using the pointer-query option at the bottom of the toolbar screen-right in the 'standard' layer at openstreetmap.org, it will be bc the search is highly localised (I don't know what radius).

Assuming you can reproduce my results, try clicking at the junction of the modern boundaries where they meet in the Witham opposite the mouth of Kyne Eau: all 3 Parts appear in my results.