What updates is 'Ubuntu Software' installing?

I have recently upgraded from 15.10 to 16.04LTS. Since the upgrade, I have still been prompted occasionally to update by 'Software Updater' which had been present in 15.10. Quite a few updates to Ubuntu core have been done this way.

In the last couple of days, when returning from suspend a popup has appeared in the same place as the wifi connected/disconnected information appears. This new popup told me that 'Important OS and application updates are ready..." before disappearing. Yet when I checked with the 'Software Updater' it told me that the software was up to date. Checking with the new 'Ubuntu Software' (update tab) told me that there were updates, so I clicked 'Install'. It didn't tell me what was being installed.

Why is there this different method of checking and why are the two giving different results?

How can I find out what the new Ubuntu Software did install ?

Edit 9th May

Again today the pop-up appeared. The 'Software Updater' showed the machine was up to date. The 'Ubuntu Software' app showed 1 update. On clicking the '1' icon it showed 1 update, namely: ubuntu-drivers-common 1:0.4.17.1. I clicked the 'Install' button and installed it.

I'm none the wiser as to why it is only shown as necessary by 1 app and not the other.

Solution 1:

They're two different programs that do similar things.

Software Updater is the update-manager package (Gnome apt) and uses the apt database.

The Software Center (Titled "Ubuntu Software") is the gnome-software application and doesn't seem to use the apt database. But if you see "OS updates" under the "Updates" tab, you can click on it (the text) and it will show you what will be installed.

Why the two show different things is probably in the way they pull their package metadata.

Also, you can view the history of installs and updates here /var/log/apt/history.log