I currently use the Amazon Kindle app on my old PC, MacBook, iPad, and Android phone. I originally began using Amazon's Kindle services on my 2nd gen Kindle several years ago.
The quandary I'm running into now is that there are 3 books which appear in my Kindle app, but which do not appear to be in my Amazon Kindle library. To be clear, these are 3 books which I assume I downloaded, for free, from the Kindle store, several years ago. But the strange thing is that they do not appear anywhere in my Amazon account. When I login to Amazon in the browser and review my Kingle purchases, it shows all of my other books, but not these 3. Likewise, when I'm in the app on my PC, MacBook, and iPad (I haven't checked on the other devices), these 3 books appear as being downloaded to the device, even though I never explicitly downloaded them to the device. Moreover, there is no option for me to delete them and leave them in the cloud. If I click delete, it asks me if I want to permanently delete them.
Now here's the tricky thing; I first encountered this issue while using my PC a few months ago before I purchased my MacBook. In the end, I ended up deleting the 3 books on my PC. As I understood it then, I was physically deleting the books from my PC and it was my understanding that they were, at that point in time, in no way linked to the Amazon cloud.
Skip ahead to today. I installed the Kindle Reading app on my MacBook and, lo and behold, before even entering my Amazon account information into the application, those 3 books were there. No other books were in the app until after I signed in with my Amazon info.
This suggests to me that my assumption about the books not being linked to my Amazon Kindle cloud library may be correct. However, the only explanation for how the books got there then is that at some point when I transferred files to my new MacBook, those books also got transferred. Not only that, but this explanation would require for the Kindle Reader app to scan my drive in search of ebook/kindle files.
I can't speak to the likelihood of the latter, but I am quite confident regarding exactly which files I transferred to my new MacBook. I transferred only specific folders and files, and would have known if these 3 books were being transferred in that process. The only way I see that the files could have been transferred to my MacBook from my old PC is if they were saved as hidden files in a folder that I transferred. Ok, this explanation doesn't sound too likely, but it at least fits. So assuming that all of these things did happen, then I would expect to be able to find these files somewhere on my drive. As a note, I did of course find them in the Kindle content folder created by the app. But what I'm getting at is that, in conjunction with my theory, I should be able to find these books elsewhere on my drive. The trouble is that, after conducting a search that includes both invisible and system files, I am unable to find these books on my drive, other than in the kindle content folder. I should mention that the 'kindle content folder' I'm referring to is a hidden folder located in the Library directory which I have never touched before today.
So, assuming that the Kindle app wouldn't scan my drive for ebook/kindle files and then proceed to relocate those files to its own content folder, deleting the old file, my theory no longer seems to hold up.
I again turn to the possibility that they were synced over from the Amazon cloud. However, I still don't see how the Kindle reader app would have loaded those 3 books BEFORE I entered any of my Amazon information. If it helps, I was logged into Amazon in Chrome when I downloaded the Kindle Reader program from Amazon. But I really doubt they could use one's browser login session in the application just like that. Moreover, the 3 books don't appear to be a part of my actual Kindle Library, nor can I find them in my Amazon account history.
In conclusion, I have no viable explanation for how these 3 books ended up on my MacBook. I'd really like to know how this was able to happen.