Yesterday I downloaded and thought I installed Sierra after being told of the available update, spending more than an hour downloading and then restarting.
I had to resign in to a few apps, e.g. Google back up and sync so it looks like something did change.
Before I made the update, if I navigated to Apple menu > About this Mac I would see the exact same screen that I see now, here it is:
10.9.5 appears to be Mavericks. From Google search:
Under Apple menu > App store > Updates, I see that Sierra was installed recently:
Am I actually on Sierra right now or am I still on Mavericks?