Limited Collectors' Edition C-31 (Oct/Nov 74) was the first of two issues devoted exclusively to Superman. This issue reprints three Superman stories from the 40s, two from the 60s and one from the 70s. Curiously, the first story reprinted is the first half of the two parter that introduced Luthor, but the second part is not in this volume.
C-38 (Oct/Nov 75) has reprints of Superman stories in which he deals with children. Two stories are from the 1940s, one of which has Lois Lane's niece, Susie, and three are from the 60s, two of which have the alien kids Ziggy and Zaggy.