Redemption codes are generated with a standard expiry time frame. Online access is provided for a total of 2 years from code redemption. Once this time frame has passed the eBook will no longer appear in your online Bookshelf. Download access via a desktop computer or mobile device provides perpetual access. The eBook can be downloaded to a computer or mobile device at any point in time once you have redeemed your code. Internet access is required for the initial download, after that the material will be available offline.
If you know that you redeemed the code within that time frame, check the date/clock on your computer. If it is set incorrectly it may affect the viewability of your eBook.