Once all customer and shipping addresses have been loaded with the appropriate tax information, you should load this information into any sales orders that were converted into the system and are therefore missing the correct tax information. The Update Sales Order Tax Information (FV060XT1) program can be used to load the Taxcode and Taxtype fields in the orders. You will not need to complete this step for new orders entered directly into the system, as the tax information is required and filled in by the Order Entry program.
More:
Load any converted invoice line items with the correct Taxcode information