I have a "client sales" sheet and a "products" sheet.
When a client buys a product i use a drop down box on the "client sales" sheet that looks up products on the "products" sheet and it returns the value of the product.

After a couple of months the product price may increase, so i have to update the cost of the item on the "products" sheet

PROBLEM
All previous sales automatically update after i update the products price on the "products" sheet.
Is there a way of stopping all old data updating and only new lookups now use the new price?