Im not sure if anyone else is having this issue, but its a big one for us. We have just noticed that if you edit a customer account, edit their shipping address then click on add/edit, if the customer has no tax number already NetSuite automatically puts the revelant countries tax code in the tax number field (i.e. UK = GB, Ireland = IE). If this customer then places an order and are in a country where they are tax exempt the system sees the prefix in the tax number field as being valid and gives the customer tax exemption.