That's interesting because I tried that:
I still had an immortal soul and opened it now as the new beast did not show in the list - BUT:
-- I play on 2 devices let's name them A and B
-- Game was started on A and I went to the book of souls. I switched off Internet, Network and even put the device in flight mode. Opened the soul and a E the Great jumped out (dupe). So I force quit the game and left internet connection off. There was no way of communicating with the server.
-- Started on B and went to the book of souls - siwtched internet off / flight mode and opened the soul - guess what? E the Great!
-- With internet off on A I deinstalled the game, switched internet back on and reinstalled -> E the Great.
I will try that again with some rare souls and probably 10 common souls as well. But it seems that at least the Immortal soul was predefined. Maybe they all are and whenever a new char comes out the souls she / he is in will be rerolled? That would explain something ... maybe somebody else wants to test that theory as well? maybe somebody with an emulator because it's faster with backing up and restore very quick.
An explanation would be very very interesting. But it's awkward so we won't get an answer ... as with all the other weird shit that's going on.