Linked Accounts with of the trail keys

Hi so today i was trying to link my gw acc. to my ncsoft acc. i tried using all of my available access keys but i kept getting an error, so then i tried a trial key and it worked.

so my question is, is it linked to my account or the trial key (never been used btw)?

A little tip if you are trying to link another account to Guild wars to your master account..if your having probs

Go to instore on the account your trying to link..

Select a purchase..lets say an additional pane

when you go to checkout you will be asked your master account

enter this and you will be allowed to link it to the master

Once done......Cancell the transaction and your other account is linked to the master

Yeah I found this confusing as hell to figure out when I was trying to link all my existing accs to a NC master acc. As the poster above says, do it in-game via the store. If there is another way to do it its either very unintuitive or very well hidden.