I’m hesitant to post this, since it makes me happy at the moment, but if you have pre-purchased PP on Epic Store and later the Season Pass, everyone knows you are locked out of buying digital extras and/or getting the Year One Edition. So mainly you could never get Living Weapons DLC if you went that route, you could not buy it again on EGS.
But now, I tried to launch the game without the Epic Launcher, and I was greeted with the Year One Edition main menu screen (which I had never seen before). Furthermore, launching a new game, I get to select the Living Weapons DLC along with the other 3 and it starts a new game fine.
So please be quiet everyone shhhh and don’t tell them! 
I hope they never fix this.