Be careful with what you do with your PC codes for Dishonored 2, as a few Neogaf users are venting frustration at a system that wasn't clear about which redeemable code would gain you access to each game in the series.
Boxed copies of Dishonored 2 come with a playable copy of the original Dishonored - just in case you're not up to speed on the series. So when players already accustomed to the series buy into the boxed version hoping to gift the first game to a friend; they're getting burned. You can't do it.
Through attempts at redeeming the Dishonored 1 code hoping for it to land in your Steam Inventory, you're met with a screen telling you it can only be redeemed to an account with its sequel currently in your library - yet upon registering the Dishonored 2 code, you're given the bundle without using the apparent original Dishonored key.
So what's it all about? You get two codes in a boxed version, of which you'd presume would be one for each game. Yet one is for both games, while the other can't be redeemed until you use the bundle code. And according to the original NeoGAF poster, the second code is for exactly the same thing - yet still can't be used without having Dishonored 2 on your account.
The end conclusion here is nobody is quite sure what the second code is for. It's safe to say you shouldn't go throwing either one at a friend right now in case you're just giving away your copy of Dishonored 2 as well. Play it safe until Bethesda shed a little more light on the issue.