Quote Originally Posted by MugenMugetsu View Post
snip
This applies to Steam codes sold upon activating the game, and grabbing the CD key from here I believe.



I might be incorrect, but the key is likely tied to your Steam account, meaning that if someone purchased that key they'd be unable to purchase expansion packs unless they got another key from the same person, even if they were to buy the expansion off Steam from their own account. I saw a Reddit thread about that not too long ago, they were able to pay through the Steam wallet so their account was a Steam based one, but after they bought Heavensward off Steam the key didn't register.