The publishing of reprints in F&SF began in the very first issue, and continued throughout its first decade. The first four issues, in fact, contained nearly as many reprints as it did original fiction (22 reprints, 27 originals). It was not until its 16th issue, September 1952, that the number of reprints began to decline. Beginning with that issue, reprints rarely exceeded 1, 2, or 3 per issue. Overall, for the first decade, Fall 1949 through December 1959, 27% of the fiction in the 103 issues were reprints (27.3%, or 243 reprints and 890 original pieces of fiction).
The reprints served a purpose, however, beyond being filler material. F&SF's editors attempted, with success I believe, to educate its readers in the history of the literature genres of fantasy, horror, & science fiction. At least 55 of its reprints were published before 1930 (30 from the 1600s thru the 1800s), and 9 of its reprints were translations from the French, German, or Russian. Quite a few of these reprints were preceded by introductions by the editors, beyond the usual story intros, to give some background about the authors and their works.
The first advertised 'all original' issue was the April 1954 issue (whole #35). Although this issue actually contains a story that was first published elsewhere, F&SF did not consider it a true reprint since it was published in a small market, or local, magazine. Likewise for its 'all original' February 1958 issue (whole #81).
F&SF advertised a total of 15 issues as containing 'all original' pieces of fiction. However, one of these issues, July 1956 (whole #62), contained 5 reprints. I believe it to have been a miscalculation on F&SF's part, because the following issue, August 1956, actually had no reprints instead, and it was not advertised as such. If the story intros are to be believed, there were 11 other issues that contained only original fiction.
The last declared 'all original' issue was the March 1959 issue (whole #94). The difficulty in planning these issues must have stopped their advertising for them, and I believe that a policy of gradually phasing in issues with only original pieces of fiction began in the late 1950s. By the early- to mid-1960s, there were only rare pieces of reprinted fiction, and these were sometimes listed in the TOC as a 'special reprint feature.' The purpose of these reprints were again to educate their readers.
After the mid-1960s, reprints were mostly stories of quality that were first published in anthologies or author's collections. These stories tended to be stories that were original to the anthology or collection. In the 1960s, 93 pieces were reprints, making up 9.5% of the fiction; in the 1970s, 59 pieces were reprints, but 32 were in the 30th Anniversary Issue (October 1979). Excluding these, only 2.8% of the fiction in the 1970s were reprints. In the 1980s, only 19 pieces were reprints (1.6%); and in the 1990s, 41 pieces were reprints (3.3%). The first year in which there were no reprints was 1975; the only other years without reprints were 1981, 1982 and 1984.
Two of the more recent reprints were reminiscent of the early years, when education of the readers was one of the editors' goals. The September 1986 issue of F&SF published a "lost" Algernon Blackwood story, "At a Mayfair Luncheon." This story was first published in Great Britain in the March 1936 issue of Windsor Magazine, and was never published in any of Blackwood's collections. In the August 1990 issue of F&SF, a story by Katharine Newlin Burt, "Herself," was published. The introduction by the editor to the story notes it is "strong and stylish . . . levels above most of what passes for 'horror' or psychological suspense these days." It was first published in Scribner's Magazine in April 1930.
Of the 2179 pieces of non-fiction published in F&SF over its first 50 years, only 10 were reprints, and two of them were published in the 50th Anniversary Issue, the October/November 1999 issue. One was labeled a guest editorial by Ray Bradbury, a fitting piece for the upcoming millennium. The other was a biographical piece about the early writing days of Theodore Sturgeon, by Judith Merril, both sadly no longer with us, which preceded a short story by Sturgeon which was never before published. Both rare non-fiction reprints were very appropriate for the occasions.
Translated Works. All of the translated works published in F&SF are believed to be reprints. There were 38 translated works in F&SF in its 1st 50 years, by 30 authors, two of them being collaborations. There were 18 translations from the French, 7 from the Russian, 6 from the German, 2 each from the Italian, Spanish, & Japanese, and one from the Czech language. Many of these translations can be considered part of the early F&SF editors attempts to educate the readers to the wide world of sf/f, as 10 of these translations date from the 1700s to 1922. The rest were mostly current reprints (at the time of publication), or the dates of first publication were unknown.
Translations appear to have been very popular during the 1950s & 1960s; the majority, 31, were published by the February 1969 issue. Three more were published in the 1970s, two in the 1980s, and two in the 1990s, the last one in the June 1998 issue.