This information applies to versions: 2018, 2, 3, 4, 5
Nik Collection apps were developed on separate timelines, so the software names of the apps are not identical to the version number of Nik Collection.
To find out, which version you have installed, open any plugin and go to the Menu > About option. You will see numbers in brackets that correspond to the Nik Collection version number.
For example:
The screenshot shows HDR Efex 2 from Nik Collection 4, version 4.3.4
From Nik Collection 6 on, all software names of the apps are identical with the version number of Nik Collection.