I posted in the Kobo thread when I should more logically have posted here.
It turns out that I can't stack my Kobo promotional credit with the SAVE50 code, so I don't plan to use the code at all. The books I wanted to use the code on are pricey and I don't feel like a significant cash outlay. Back on the wishlist they go. I've got plenty to read and if a much better coupon falls in my lap, I'll reconsider.
At Amazon, I used my expiring promo credit plus my no-rush credit to buy three books. A slight cash outlay so as not to leave any credit on the table, so I'm considering them essentially free and they don't count.
All of this means I'm exiting August unscathed.