The excellent crossword-puzzle documentary Wordplay (2006) goes into that a little. We have it on DVD, but without having to go dig it out, I’m remembering it interviews a crossword-puzzle-master lady who interned under one of the pioneers, who also decreed there could be no isolated areas, no little “word islands” completely cut off from the rest of the puzzle.
The movie also has Bill Clinton, Bob Dole and Jon Stewart talking about their love of solving these puzzles. Talks to Will Shortz, the editor of the New York Times crossword since the early 1990s and who has a university degree in games. Quite an informative little film.