1 - Your REF will discover that my discount is higher AFTER using your ref, because i've written only in my last replies (and not in the title or in the OP) that i'm giving a discount.
AND i'm sure (because all people are doing this way) they will ask me "But the Discount using REF XXX Is comulative with your discount?"
2 - As i told in point 1, user will continue use your ref, even if discount is not cumulative, and you continue get your 0.1, that is probably the most important answer to question 2.