Missing .mbp file for books on kindle (PW)

[vamarci]

Recently I wanted to remove most of books from my Kindle Paperwhite (1st gen) because I just had way too many books that I haven't been reading for quite a while, yet I didn't want to lose the notes I made, the highlights and most importantly, the location where I was at the last time of reading. So with the help of Google I managed to figure out that it is the .mbp file where such information is stored for each book. When I wanted to follow the instructions in this thread on how to import my annotations into calibre I had to realize that many of my books were missing the mbp file, in fact some of my books had only one file on the kindle, the book itself (azw or mobi). This is quite strange because I was definitely reading such books which had no other files. So I tried copying the whole folder in which the file was contained and then copy back, and the every information which was on the device before (last page, highlights etc.) disappeared.
I know that I could use the cloud solution by emailing my books, but I prefer having my books in azw3 instead of mobi.
So could anyone help me out? Where are all the infos which I want to integrate into calibre stored? How to proceed if the tutorial in the thread I've linked is not working?

Thanks!