Regeneration is rebirth. . .from spiritual death to spiritual life in and by the sovereign choice of the Holy Spirit (Jn 3:3-5) whose sovereignty is as unaccountable as the wind (Jn 3:6-8).The OT saints are saved via faith. Faith that God will provide a future savior. I'm not all sure what you mean about "regeneration" but we know the Holy Spirit wasn't given to the believers until the day of Pentecost.