DD official reply
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The 20% coupons do not apply to Books, CDs, Electronics or Video Games.

However, we have discounted nearly 150,000 books and 15,000 CDs an additional 20% off for this sale. Those titles are marked with a "Mega Sale" logo and the price shown on the site is the discounted price--no coupon is necessary to get the discount on the titles marked with a "Mega Sale" logo. All of these titles will appear on the site on June 1 and there will be rooms for you to sort through the Book and CD titles on sale.