There is definitely a need to clearly state what the reference number is for a number of reasons.
Purchase Invoices. It is then more clear to inexperience novice business owners using Manager what reference number one is supposed to be putting into that field.
With sales orders - read this discussion and you will see the whole point of the need to clearly state what reference number is to be used in sales orders. - Sales Order Status Problem This topic is a classic example of why the reference field needs to be defined in order to avoid the precise problem that Compuit and myself are experiencing.
Lubos has just stated that he believes that the sales order number is the customer purchase order reference number! So documentation and the program should support that otherwise constant ambiguity is the only outcome here as witnessed in the aforementioned linked topic.