Originally Posted by HarryT
That's not necessarily the reason for revision. The out-of-copyright versions of "modern" SF are almost always the original magazine stories for which copyright was not renewed. It was entirely normal for the stories to be re-written somewhat when republished as novels (which are still under copyright protection). You'll find the same if you compare the magazine versions of E.E.Smith's early "Lensman" books (for which the magazine copyright wasn't renewed) with the novel versions of the same stories.
I'm pretty sure in this case that the revisions are recent -- the collapse of the Soviet Union, the moon landings, and our failure to continue manned space exploration after the moon landings are all in the Baen edition from 2000, and the previous edition was published in 1979, when nobody much was predicting the end of Soviet power.