Complex sentence: After Kornbluth's death, his widow turned over his story notes and drafts to Pohl, who completed a dozen or so stories based on this material, most of which were eventually collected in this volume and in the later "Critical Mass".
Split into simpler sentences: After Kornbluth's death, his widow turned over his story notes and drafts to Pohl. Pohl completed a dozen or so stories based on this material, most of which were eventually collected in this volume and in the later "Critical Mass".