Automatically tracking the Sales and Purchases orders is a feature that must eventually be added to Manager.
It does introduce some complexity in the programming because things don’t always go straight as we want it to go when we work with purchase orders and sales orders.
Some programs have features used to make changes to orders for example and that order becomes a change order which will have the original order number and it own change order number stated on it.
When an invoice copied from an order gets edited the system will ask if it a permanent change, if it a permanent change the system closes the order and report the order as closed. if the order is still open, the order status becomes partially fulfilled, order exceeded or order not same as invoice(s)
In serious business environments orders are not likely to be different from it subsequent invoices and if there will be such a situation, a change order will be issued which represents the new order agreements and makes the original order inactive or closed.
In a serious work environment there are workflows. And people are expected to do things the right way. (e.g. You may disallow entering of invoices without correct and open order numbers, or limit limited users from raising invoice from the invoice tab which requires manually entering order numbers or the system suggests for the user to select the right order number to avoid errors )
There are plenty more things that can be done to add order tracking features, it will be a huge plus as people are paying for big software out there just to handle the complications in these things (orders and inventory available for example).
I Know @lubos himself has a plan for the future for order tracking.
We need to start somewhere and develop it bit by bit.and