According to the last customer representative I spoke to…
You are able to redownload your books an unlimited number of times to any specific device.
Any one time the books can be on a finite number of devices. In most cases that means you can have the same book on six different devices.
Unfortunately the publishers decide how many licenses, that is devices, a book can be on at any one time. While most of the time that will be five or six different devices there will be times when it’s only one device.
At the present time there is no way to know how many devices can be licensed prior to buying the book.
According to the customer rep, there is a project to try to get that information available to the customer, but it’s not yet available.
Finally, when you have reached a limit of six devices and you swap one older device for a new one, it does not automatically reset the number of licenses so you can add the new one. Amazon can release all of the licenses which will remove any given book from all of the devices and then allow you to re-download it that same number of times.
In other words, if his information was accurate, and the runaround I got this afternoon does make me continue to wonder, once you purchase a book you will have access to it going forward.
Tip: You might want to back up your Amazon downloads on your PC via your Kindle’s USB cable. But then we know about hard drives. This is hardly a perfect solution. Let’s just hope Amazon keeps its word.