Another factor is that during the war, the government set a limit on the number of releases each record company could issue each month. There were therefore not many new records being released, allowing the more obscure artists (Beryl Davis, Phyllis Robins, George Elrick etc.) to sneak into the chart. Indeed I suspect at times the number of (popular) new releases that didn't chart were in the minority! Turner Layton issued a record pretty much every month (sometimes two) for the entire duration so it's not surprising a lot of his made the top 30.