Hello there, @leeia.
I can definitely share some insights about this item question. When you update the sales price, this will not update the entries you created prior to the change. The sales order, for example, will retain the value of the old sales price even after changing it.
This means, that changes to the cost or selling price will directly affect future transactions. See this link for more information about updating item details: Add, edit, and delete items.
Post here again if you need further help with your inventory processes. I'll be right here to help you out.
