Sierra Cosmos On-Line is a software industry mega-giant originally known as Sierra-Online back in the late 20th century. While rumored to have gone out of business by early 21st century, Gir Draxon predicted they would at some point finalize acquisitions of IBN, Macrosoft, and Garden Weezil in the year 3010.
Sierra was actually quite active in both eras as a publishing house it was producing games and selling them to people of the past and future. It also was known to publish Galactic Inquirer and Popular Janitronics and Space Piston Magazine (and older Sierra and InterAction magazines) in the past on earth (back in the 1980 to 1990s), and ship the recent issues to its readers in the future. Many of these periodicals proved useful to Roger in the future.
Space Piston is listed to be published by Sierra (although its location of publishing is not known), and Popular Janitronics location is known, but not necessarily its date of publishing. Each of these magazines are known for publishing Sierra products (and a number of its editors were Sierra employees). It's not known if the Sierra (Newsletter and News Magazine) and InterAction were ever published in the future, but they were at least publish a few articles and material from Roger's era.
In 1986 and 3003, Sierra published Space Quest I: The Sarien Encounter (original version).
In approximately 1987 and 3004 they published Space Quest II: Vohaul's Revenge.
In 1989 and between 3006 and 3009 they published Space Quest III (around the time or after the Two Guys were kidnapped by Sierra's sometimes rival sometimes official distributor ScumSoft).
In 1991, and perhaps in the 24th century or later (ya it might be out of order) they released SQ4, and the SQ4 Hintbook. It is rumored that a competitor or subsidiary Sahara Off-Ramp released Dacron Danny Does Dirty Deeds in the Dark Wearing Drip-dry Duds around this time as well, and Stunt Flyer was released or reissued as well.
In 1993 and 3009/10 they released Space Quest V (just in time to take advantage of the adventure Roger Wilco was currently involved in at the time).
In 1995 and at some point between 3043 or sometime after 3057 Space Quest 6 was released.