First of all, I have to say I’m not using codes myself. I’m pretty advanced in the game and the rewards from codes make little difference to me, so I’d rather leave the codes for newer players.
Someone from my guild was having problems activating a code, and then another member did it for them right after having activated the same code for himself. That made me think: The way codes work now, nothing stops anyone from activating the same code multiple times for other people, like all members of the their guild. I even saw someone in global saying they’re claiming the code for their guildmates, like I thought.
Unless I’m missing some kind of limitation, I personally don’t think this system is fair. It will make codes be completely used up really quickly, while leaving other people with no bonuses.
I can’t really think of a good solution for this right now. You could ask for people’s password, but I think only people who have linked their accounts to an email address have passwords, so that might be an issue. But I do think this is an issue and bringing this up might make someone come up with a better solution.