Thank you very much.
So the Byzantium is the latest and rolling one while the one that is available on the PureOS website is the stable one that once upon a time was the rolling one! 
Did I get it right? lol
It is not that I mind that much about what is the name of each release or what exactly is the practice that PureOS’s developers follow. I just wanted to know how long each release is supposed to be supported in order to avoid reinstallations on the SSD disk. These disk are somewhat more “sensitive” than the other ones particularly if you repartition them. I installled already something that didn’t work for me and that is the reason why I formated the disk and I 'm looking for something else.
I know about PureOS approach regarding software freedom because I came directly from the gnu.org distro page to that of puroOS.
I mean I checked the list of the distros and downloaded a couple of live iso images to test and decide.
I have made up my mind that I need one that is rolling and also debian based in order to be compatible with some third party but working drivers that I have available for my scanner.
I thought originally and just for the sake of change to install an Arch or Arch based distribution but then I remembered that I have to make the scanner work and I changed my mind and decided to go for one with all free software, that either way I use on all the rest of the applications that I run on my pc.
Thank you very much for the information. 
ETA: Irrelevant. But what is Plasma? New GUI on the block?? 
I like GNOME and Mate. These are ny interchangable GUIs. as both work for me the same.