1.17 is the last version of K4PC where you will be certain to obtain a book that can be imported into Calibre. 1.19.x allows K4PC to work with "Enhanced Typesetting" books (KFX) which at this time can't be used outside of Amazon's ecosystem.
Find some more info here...
https://www.mobileread.com/forums/sh...d.php?t=282412