When the item is already showing on one of the recommendation boxes, it should not show on the other recommendations. LimeSpot does show duplicate items on the same page as it defeats the purpose of personalizing the shopping experience for customers.
Here are the exceptions:
Recent Views and Upsell boxes are completely ignored in this formula
Cross-sell items take priority (since they are manually picked up and need to stay)
Other boxes are processed in the order by which they are displayed on the page