The quick “tl;dr” version — updates don’t work, but updating is still possible.
I installed kubuntu-16.04 in April. Although I don’t use it much, I occasionally boot into it to check a few things. Whenever I booted into Kubuntu, I looked to see if the update applet was notifying me of updates. I left the system running for an hour or more, to give it plenty of time to find out.
It never showed any updates.
So I clicked on the applet (hidden tray icon) and asked it to check for updates. It told me that my system was up to date.