Small oversights can pull people out of your story, so making an effort to get even the most inconsequential things right can reap big rewards.
Great points. Reminds me of a horror novel I was reading that had some teen characters (who were about to die) listening to AC/DC's Thunderstruck in 1985. But of course that song came out in 1990. I don't know if I finished the book.
Great advice, Johnny. We world-builders must be sticklers. For this very reason, some people--including myself--have problems with alternative history. What if the Nazis had won? They didn't, so--