Virtually every date on the timeline is verifiable and has been researched through public records, or through reliable published sources.
In the cases of video game release dates, many of these dates are the “first use in commerce” dates filed with the United States Trademark & Patent Office, or “dates of first publication” from the United States Copyright Office at the Library of Congress. This also provides the release dates used for some toys and other products. A “first use in commerce” date or “date of first publication” is generally the date at which a given product first became commercially available to the public.
Many of the dates involved in the parts of the timeline related to video game history come from widely published press releases, and the resulting articles reprinting specifics of those press releases, in major publications’ business sections. The archives of the New York Times, the Los Angeles Times, and the Wall Street Journal were particularly invaluable for such dates and the events involved.
Many of the dates involved in the parts of the timeline related to space history are a matter of public record through NASA and the National Space Science Data Center archives (which record details of every space vehicle ever launched – trust me when I say that it was a sanity-saver to include only the most interesting and notable space events on the timeline, though I tried to include every manned mission and every major robotic space probe ever flown in space – as well as some also-rans that never got to finish their mission objectives). In some of the more obscure cases, I trawled the publicly available NASA press release archives.
Broadcast dates and movie premiere dates are usually reliably represented on IMDb, though I try to double check these through available archive sources (vintage TV Guide listings, etc.) before “going public” with them, either on the timeline or in the site’s episode/movie guide section.
Real, verifiable (and easily duplicated) research went into this project, and given the nature of the sources involved, I stand by the research as solid.