Maybe I'm wrong, but don't stress over these codes. I don't remember how story mode was since I only played it once and did RAID mode, but these unlocks so far are essentially useless. They may help in the very beginning of RAID mode, but the beginning of RAID isn't hard.
Basically, these are low level guns, like 5 is the highest so far I think. You'll be discarding these real quick since you'll get way more powerful guns later. And you'll need them.
But that's the 3DS version or maybe there's something else I'm forgetting. Basically, when you see like a lvl 50 gun code, THAT'S the one you wanna get.
Still, I'm unlocking these anyway so I appreicate everyone's contributions.