The fact of the matter is that Calibre 2.75.0 arrived two days before Christmas Day, but the small 2.75.1 bugfix release landed a couple of days later, on December 25, 2016, to address a regression in version 2.75.0 that broke the Live CSS feature in the editor, which might have also caused various other minor issues in the viewer. However, the biggest new features of the Calibre 2.75.x release is support for new 4.2 firmware version for Kobo e-book readers, along with the ability to user the amazon_com, amazon_au, and amazon_in identifiers in the Book details panel. Of course, lots of bugs reported by users since Calibre 2.74.0 have been resolved.