Where Are My Cover Pages????

I have been purchasing books from Google Play and downloading them to Adobe Digital Editions. But some of the ebook cover pages don't show up. These are ebooks that have been paid for WITH cover pages, but a few of them are missing the cover pages. Can someone tell me what I'm missing? Is there something wrong with the software? I've never had a problem with downloading ebooks until I started using this software. Why am I missing cover pages????