I found where the difference is. For 2 items (bought at the same time, entered the stock at the same time, invoiced and delivered to clients at the same time) the two Purchase Invoices for their transport costs have dates that are earlier than the Sales Invoice through which we sold them. This is because sometimes our logistic company gives us credit and invoices us once the goods are delivered.
This creates what I mentioned in another post as “ghost lines” with 0 values.
The costs related to transport gets then allocated to the COGS and in it appears with the description “Quantity on hand for this item is zero. Value on hand automatically transferred to expenses.”
But these specific costs do not appear in the Value Movement Report.
However, if the quantity on hand does not become 0, the “ghost line” do not appear and the figures for an item in the COGS and the Inventory Movement Report match:
I understand there might be valid reasons for this, but it is quite normal, I think, that suppliers issue invoices much later than when their services/products are supplied. I think this should be taken into consideration too.
Now I wonder whether these values that are not used in the Inventory Value Movement Report are not taken in consideration even in the Inventory Profit Margin Report?