I remember reading the original Hardy Boys books in the 60s, but when I went to reread them a few years later I found they had been rewritten to remove references to firearms and other things.
Some Hardy Boys have been rewritten numerous times. I have read that the first set of rewrites "dumbed down" the books, by reducing the reading level by something like four grades. Some of the updating, -- removing references to telegrams, not having Frank and Joe meet spritely Civil-War veterans -- probably helped keep the stories fresh for kids. But they also turned Frank and Joe into good two-shoes who refuse to exceed the speed limit, even in an emergency. But in one early book, Tower Treasure, I think, Frank and Joe created a hoax bomb to district the police!