A lot of times, what appear like science errors now, weren't errors when the stories were written. Lots of authors, like Niven ("The Coldest Place") and Asimov (Lucky Star and the Big Sun of Mercury) had Mercury as tidally locked to the Sun. Niven also had a story (The Hole Man) about a small black hole, written between the publication of the idea that small black holes could have been created during the Big Bang, and the publication of Hawking's theory of black hole decay, which made the story impossible. Heinlein was actually writing early enough that the accepted number of human chromosomes was 48.
The idea that RNA is the mechanism for memory storage, and thus could be used to transfer memories from creature to creature, was popular in the 1960s but discredited in the scientific community by the early 1970s. However, science fiction authors continued to use it into the 80s and 90s. In some cases, an author who built memory transfer technology into his or her universe's background, was stuck with the error - like Larry Niven in the State universe.
Authors sometimes go to the trouble of fixing old errors - especially if it gives the chance to write a new book.