1925, April 26, Book of Rules. Courtesy of Jerry Britton. (Scan pending.)
Lin Bongaardt believes the next edition was in 1941, though there likely would have been changes issued by sticker or General Orders in the Employee Timetables.
1941, Sept. 28, Book of Rules. Dated 1941, but stamped for Feb. 1, 1946 and Sept. 28, 1947. Courtesy of Jerry Britton. (Scan pending.)
Lin Bongaardt explained on PRR-FAX that the 1941 edition was in use until the release of the 1951 edition, but was reprinted four times -- 9/16/1943 (tan cover, like the original), 2/1/1946 (tan cover), 2/1/1946 and 9/28/1947 (tan cover), and 9/25/1949 (salmon-color cover). He adds that "It appears that the different editions were used in parallel (in some cases, an earlier edition that I have contains stickers for changes subsequent to a later edition)."
1951, Sept. 30, Rules for Conducting Transportation. Courtesy of David Wartell.
1954, March, Rules for Conducting Transportation, dated 1951 but with inspector's stamp certifying it through March, 1954.