That memory places the earliest known kidnapping of the Runecarver to be year 8, the year the Lich King was created. Assuming the Jailer ripped the plans for the Domination Armor and Frostmourne the same year he kidnapped the Runecarver then the Runecarver could have been
Draka arrived in the Shadowlands in Year 1. So Draka could have known and worked with the Primus for 7 years before his disappearance, and if Primus is the Runecarver it would mean he's been chained up for 25 years. Runecarver being the Primus works fine, unless the Primus disappeared very recently.