Somebody like Hal CLement will figure it all out with a slide rule and equations. I just read what's in the NY Times. This is a moderated chat. If you have a question for our panelists, please send it to me, Moderator, as a private message. . Well, it can be reconned by a sufficiently dedicated fan, but still.
History can overtake a plot too.
Tom Clancey's world, e.g., went south when ther USSR went down. Unfortunately it didn't destroy his literary career. Even when writing a medieval world, its tech must be consistent. I doubt there's much real difference. Although in staight-up SF, the rules are already there to the knowledgeable reader, at least to a degree.