I've experienced an issue where you lose a blueprint for a weapon you've redeemed if you dismantle it, without taking it out of your bag. in my case it was the spectral baseball bat, since you get it at lvl 1 I dismantled it. I later found out I didn't get the blueprint because I never took the weapon out and into my inventory.
#Losing Blueprints.
old gale
velvet tangle
Best you can do is rollback your save or start a new one (if you are not too far). But agree, I spend 1 hour to find out how to get these blueprints.