the even shorter version:
tablet B was off when the book being added to calibre, the book being edited from version A to version B
tablet B was then and only then turned on, yet it acquired Book version A from content server.
at no time, in this universe ,was Tablet B switched ON , while book version A existed as a file in my library.
i will refer to it henceforth as Schrodinger's tablet
Cat says it might be valuable but he will not be sitting on it / in it/ near it any time soon