No no, those are picture from an old release. They are before the 'open' version, when there default was 4 groups of each 16 channels. The 'a,b,c,d' allowed users to switch between these hardcoded groups.
Current release has no limits to the number of channels, and the mixer 'rack' only shows the channels, that has been made by user.
It is likely that some kind of groups will be possible in a later release.
You can see and learn more about using the 'modern' LMMS mixer here:
https://www.youtube.com/watch?v=BCbel56VuEU