As I did receive no answer, I did move (*1 one of my both full installations to the big partition I did first dedicate as my main partition for Netrunner rolling and install Netrunner rolling itself normally in the little one were the other system was first installed.
I know now the answer: Netrunner running doesn’t erase somewhat excepted you would mark it has to do that…
I have now a beautiful installation from Netrunner rolling in that little partition and I am happy. I hope that the other system (Debian SID) will start again if I can mix those of the files out /var not being moved!
(*1 some files, not all, from /var did not move willing. It is bad because the most of them are icones and they are hundreds to move now merging with those already moved without difficulty. I hope I will find a way in the next days to move them…
Sorry for no answer, but I’ve been a bit under the weather the last few days.
I’m also glad that you were able to figure it out on your own, kudos to you.
Welcome to the community.