questions about the way invoices are organised in IPS

[LiquidFractal]

I'm beginning to use the Invoice feature in a more meaningful way, and find it disappointing that site owners are unable to set their own invoice code numbers.  Yes, there is the PO number, but what I don't understand is why it's editable by customers/clients?  What would be the point of that if you want to assign invoice codes for your own records?

If there is some other reason why customers/clients are able to edit the notes and PO number, I'd love to hear it because frankly it doesn't make sense to me that I, as site owner, cannot set an internal invoice code/ID which cannot be touched by the customer (not to mention notes).  Am I missing something?