I just found this key in a saved word document of my unused keys, i already own it. Trying to redeem the key on steam leads to borderlands install. Not actually sure if it's GOTY edition or standard edition. My notes say "Borderlands and Borderlands DLCs:
The Zombie Island of Dr. Ned, Mad Moxxi's Underdome Riot, & The Secret Armory of General Knoxx"