Once you have added an inventory item you can attach a pricing Co-efficient to the item.
Download the Inventory group, the list will contain inventory items that have a green background, this means that no pricing co-efficient has been added at this stage
When adding (A operation column) pricing to new Inventory Items you need to enter a Date in to column E The date here will apply to any orders from the date. If you enter a date in the past any orders that contain this inventory item will have the new price added.
Leave the PKID column (A) as is.
Note if the spreadsheet is not green and contains a unique number in the PkId Column a Price already exists, you can add a new one but you must ensure the date effective has been updated.
Try to not back date pricing co-efficients as it may affect previous orders in that date range.