In the late 1990s I implemented an algorithm from one of Knuth's books. (An algorithm to generate prime numbers.) I found a mistake! I was so excited. I then

In the late 1990s I implemented an algorithm from one of Knuth's books. (An algorithm to generate prime numbers.) I found a mistake! I was so excited. I then checked the errata. It was known. It took another 20 years before I found an actual mistake, regarding the early history of superimposed codes. A very specialized topic where I have one of the few copies of the patent challenge distinguishing between random superimposed codes and arbitrarily selected superimposed codes. I have a check.