It is not easy to create and track a BACK TO BACK especially if there is specific information required and not a standard stock code. for example you have a standard stock code that you only have made especially to order - the details are identical except perhaps the colour or locks so you create a sales order with the common product code and tweak the description to blue number 123456 (as you perhaps offer all the range of colours that are available in paint) - you now want to create a purchase order and do not want to re type 20/30 lines - you cant!