Grrr! I may have stumbled across the version answer and shouldn't have asked that question.
Code:
calibredb --version
calibredb (calibre 3.13)
Although why the confusing:
Code:
sudo apt-show-versions calibre
calibre:all/zesty 2.75.1+dfsg-1build1~1 uptodate
But it still leaves my problem of access to the /opds xml file that started this.