I've heard at least one actual numbers station, tuned correctly, personally. Kind of weird to think of the spy sitting there and decoding it somewhere. If you cruise the shortwave hobbyist websites you can hear actual numbers stations without all the junk that the maker of those videos threw in. Once upon a time, spies used something called a one time pad to decode the signals. One time pads were so secret that nobody outside of the intelligence agencies really knows even today how they worked. There has long been a rumor that the CIA made a pad that would turn to chewing gum when dunked in water. If anybody starts talking about pads today, you know he's out of the loop. Spies today hook their radios up to laptops, which contain computer programs that translate the numbers into text. When a Cuban spy was caught around 2003, it was found that she had a dongle that connected the earphone jack in her radio to the USB port on her laptop, which had a program to translate the signals into Spanish.