It would be great if a credit note could be matched to an invoice that has already been published to Quickbooks. Much in the same way that an invoice can be matched to a purchase order a client has created.

That would be helpful because QuickBooks' way of applying a particular credit note to a particular invoice is inefficient and can often cause errors in the way payments are allocated. To match a bank payment to a group of invoices often requires time invested if there are a number of credit notes to apply.