Hi LizSnay,

Thank you for following up on this. I'll be happy to add more details.

QuickBooks follows the First In, First Out (FIFO) concept, so the realized cost of the sold item will always be based on the purchase cost. Therefore, if your client bought the item on 3/16/21 and sold them, you only need to edit the cost of the item in the purchase transaction on 3/16/21.

Changing the starting value of the item itself has no effect on previous transactions. The cost revaluation should be done on the purchase transaction (bill, check, expense)

Let us know if you have any other questions in mind. We're just right here to help you with your inventory.