Comment 75 for bug 1560797

@Brian Visel - The way the release upgrader works is that it downloads a tarball of ubuntu-release-upgrader for the release to which you are upgrading. Subsequently, the fix doesn't need to be in the release from which you are upgrading. Additionally, using "apt-get dist-upgrade" bypasses the ubuntu-release-upgrader process altogether and is not a recommended way to upgrade.

https://wiki.ubuntu.com/XenialXerus/ReleaseNotes#Upgrading_from_Ubuntu_14.04_LTS_or_15.10