I linked demand to an item, but the sales history isn't being loaded - why?

Is this item a component?

With components, you don't need to link demand because the sales are actually recorded against the finished goods, and the demand & sales history are calculated via the Bill of Materials.

So as long as the BOM is updated to include the new component then this should be populated (you may need to re-import your BOM, or select the "Load Bill of Materials" option next time you sync with your inventory management system).

OR

Does the item you are linking from already have sales history? By default, when you link demand, only sales orders that are earlier than the first order for the item are included from the linked demand item.