I am unclear if this is two separate questions, or the same question asked twice. The first question appears to be a question pertaining to locating 2 books transferred from a computer to a Kindle via USB, and the second appears to refer to 2 books from Kindle Unlimited that were also transferred from a computer to a Kindle via USB. As both Kindle and Kindle Paperwhite are tagged, I will address both as they are not the same.
Whether it is a book you own or a Kindle Unlimited book, transfers are the same. Just remember that you don't own the KU books and there is a cap on how many titles you can have at once. Hopefully, I can be of some help, though.
After downloading the books to your computer you can transfer the files via USB from your computer to the Kindle's Documents folder, then click on "My Library" at the top left of your screen and your files should appear in the "Downloaded" tab.
Kindle Fire Instructions:
After downloading the books to your computer you can transfer the files via USB from your computer to the Kindle's "Books" folder. Then, on your Kindle Fire, tap the Books content library from the top of your screen, choose the "Device" tab, and your Kindle content should show up.
Just remember that EPUB, Mobi and DRM-protected files are not supported file formats, and not all Kindle content can be transferred. If you do have unsupported files you want to place on your Kindle, you can easily convert those files to AZW or PDF for free using http://ebook.online-convert.com/convert-to-azw3. I use this exclusively for my business and there is nothing to install, no pop-ups or malware, and it's much quicker than Calibre, which you have to download.