Hello Treasure,

If the Credit note does not refer back to the Original Invoice, the Most Recent Cost appears as a default cost for the Return. However, if you edit the Unit cost, the edited Unit cost is passed on to the Item with an increase in Quantity on Hand.

If the item is not being returned to Inventory for resale, you should uncheck the ?Return? option in the item detail on the Credit Note. This way, the stock levels and costing for the remaining items will remain unaffected.