Seriously I have read your PDF twice and don't believe my usecases work correctly. If they do, please explain me, how it works.
How would that work: He sends 1 product back, but he doesn't deserve a full refund? IMO it doesn't work cleanly with partial refund as the product is not saved as returned... And the order-slip values are very strange. All values are minus. The total stays the same. I have no idea if this is wanted, but adding a discount has a completly different impact. How can adding a discount and adding a refund (with the same value) have completly different order-slip?
And I dont even start to combine this issues with ASM where you have a field like usable_quantity. Where is it good for, if not at product returns?