Writers of the 21st Century

Number in series based on LCCNs for the most part. Vance volume was definitely the sixth, based on list of available volumes on its half-title page, and Heinlein was the third based on a blurb on the back of the Vance dust jacket. Three planned volumes were probably never finished, those for Silverberg, Lem and Sturgeon which were listed as "in progress" in the list of available volumes in the Vance publication.