Diablo cd keys dont hold onto the battle net accounts.
They do now, but if you've not used these in ages you can be excused for not knowing that.
Edit: BTW, we don't mean the Battle.net game login, where your characters are stored - we mean the Battle.net where you download the "cracked" versions of the games for free if you possess the CD keys. Those are most definitely tied to the keys and if these keys have been redeemed already they're worthless.